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  • 1985-1989  (30)
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  • Synthetic methods
  • 1
    ISSN: 0570-0833
    Keywords: Metallo-ene reaction ; Ene reaction ; Synthetic methods ; Catalysis ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Metallo-ene reactions, hardly recognized until very recently, have experienced a breathtaking development when applied in an intramolecular sense. Efficient regio- and stereoselective magnesium-ene cyclizations have served as a cornerstone for numerous syntheses of structurally diverse natural products (e.g., sesquiterpenes of marine or plant origin, alkaloids, fragrances, insect defense compounds, and a fungitoxin). A brilliant example is the synthesis of the elusive odorant (+)-khusimone which outshines 20 years of work in the field of tricyclovetivane synthesis. Palladium-, platinum-, and nickel-catalyzed versions of the metallo-ene reaction are in a comparatively early stage of exploration, but, nevertheless, reveal intriguing potential. Hence an almost 100% stereospecific C—O→C—;Pd-→ C—C chirality transfer permits simple and selective, cis- or trans-annelation processes. The mild cyclization conditions are compatible with various functional groups, such as nitrogen moieties, which offer interesting perspectives for the preparation of heterocycles (e.g., alkaloids) difficult to obtain by other methods. Carbon monoxide insertion reactions of the cyclized σ-metal intermediates were shown to afford annelated cyclopentanones and cyclopentenones with concomitant stereocontrolled formation of four carbon-carbon bonds. These and other observations, highlighted in this article, provide a platform for further extensions and applications of this powerful method in organic synthesis.
    Additional Material: 11 Tab.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 716-734 
    ISSN: 0570-0833
    Keywords: Gene technology ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oligonucleotide synthesis, until a few years ago the rather exotic preserve of a few experts, has become an integral part of the arsenal of molecular-biological techniques. The last decade, in particular, has seen unbelievably rapid development in this area. DNA synthesis has been automated and can now produce genes greater than 1000 base pairs in length. Tailor-made synthetic genes also permit the synthesis of altered or even novel proteins (de novo protein design) by gene-technological methods. Together with modern methods of gene isolation, sequencing, and expression, gene synthesis has played a major part in the enormous advances achieved in gene technology.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 1173-1192 
    ISSN: 0570-0833
    Keywords: Cyclization ; Allylic alkylation ; Alkylation ; Synthetic methods ; Palladium ; Catalysis ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The history of ring systems in organic chemistry parallels their synthetic accessibility. Transition-metal-catalyzed cyclizations offer a new opportunity to create carbo- and heterocyclic compounds with great facility. Among these methods, allylic alkylations catalyzed by palladium have proven unusually productive because of the extraordinary chemo-, regio-, and diastereoselectivity and the continuing possibility for the development of enantioselectivity. The rules for ring closure differ from those for non-transition-metal-catalyzed reactions. A major benefit is the ability to generate medium (eight-, nine-, ten-, and eleven-membered) and large rings in preference to normal (five-, six- and seven-membered) rings. With the appropriate substrate, efficient macrocyclizations are possible under conditions of normal concentrations. A second major benefit derives from the complementary stereochemistry of the metalcatalyzed substitution (net retention of configuration) compared to non-metal-catalyzed reactions (inversion of configuration). Further, the requirement for the substrate to conform to the transition-metal template may impose a stereochemical preference in the intermediate that ultimately translates into the thermodynamically less stable organic product regardless of the stereochemistry of the starting material. While more work has focused on carbocyclic synthesis, the possibilities for heterocyclic synthesis are just beginning to be tapped. In addition to forming heterocycles by C—C bond formation, use of a heteroatom as a nucleophile has already proven effective for oxygen and nitrogen, with other nucleophiles awaiting investigation. New dimensions for cyclization via allylic alkylation arise by generating the requisite π-allylpalladium intermediates by methods other than palladium(0)-initiated allylic ionizations. In addition, metals other than palladium will clearly expand the possibilities, but as yet remain untapped.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 695-707 
    ISSN: 0570-0833
    Keywords: Enantioselectivity ; Lipases ; Synthetic methods ; Enzyme catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantioselective biocatalysis in nonaqueous media is becoming increasingly important in preparative synthetic chemistry. This article discusses (1) the general catalytic properties of enzymes in nonaqueous environments, (2) the basic principles that govern lipase-catalyzed enantioselective esterification and transesterification reactions in organic media for the preparation of optically active acids and alcohols, (3) the determination of kinetic and thermodynamic parameters, and (4) the quantitative analysis of published data.
    Additional Material: 5 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 28 (1989), S. 969-980 
    ISSN: 0570-0833
    Keywords: Stereoselectivity ; Reaction mechanisms ; Synthetic methods ; Free radicals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regio- and chemoselectivities of free radical reactions are often high and largely predictable; systematic studies have now shown that the stereoselectivity of free radical reactions can also be directed. Examples involving five- and six-membered cyclic radicals will be used to show how steric and stereoelectronic effects influence the diastereoselectivity of reactions of cyclic radicals with olefins. The temperature, the solvent, and the nature of the radical scavenger used also play a role, so that, if the correct reaction conditions are used, the stereoselectivity of reactions for cyclic reactants can be very high. Lower stereoselectivities are often observed for reactions between acyclic radicals and acyclic alkenes. However, preliminary experiments have indicated that under certain conditions such systems can also react in a stereoselective manner.
    Additional Material: 9 Tab.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 679-682 
    ISSN: 0570-0833
    Keywords: Reduction ; Hydrogenation ; Hydrocarbons ; Carbon ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For the synthesis of organic compounds, reduction is an indispensible reaction type which is also widely used on an industrial scale. In industrial processes hydrogen is usually used as reducing agent, since strong reducing agents like alkali metals and hydrides can only be used to a limited extent for safety and economic reasons. Very economical reducing agents that are convenient to handle and have high potential application are hydrocarbons in presence of carbon. Hydrocarbon/carbon systems can be readily used instead of molecular hydrogen and expensive metal catalysts for the hydrogenation of compounds containing, for example, CC-, CO-, or NO-double bonds. Furthermore, these systems can be used for carrying out reductions which hitherto required strong reducing agents such as zinc, tin, alkali metals and hydrides. Especially suitable as economic sources of hydrogen are refinery products such as vacuum gas oil, fuel oil S or vacuum residue oil. Hydrocarbons are dehydrogenated to unsaturated systems and finally to carbon.
    Additional Material: 2 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 797-827 
    ISSN: 0570-0833
    Keywords: Cyclobutanes ; Cyclobutenes ; Synthetic methods ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemical reactivity of cyclobutanones and cyclobutenones is considerably different from that of cyclic ketones with larger rings; this is due to their ring strain of ca. 25 kcal/mol. Detailed knowledge regarding the influence of this ring strain on regio-, chemo- and stereoselective transformations of four-membered ring ketones is of particular importance. While several reactions, such as the Baeyer-Villiger reaction, the Beckmann and Favorskii rearrangements and cine-substitution often proceed in a manner specific to four-membered rings, other reactions such as the facile ring-opening by nucleophiles, the rearrangement to tropolones, the thermal [2+2]-cycloreversion, the isomerization to vinylketenes and the photochemical formation of oxacarbenes are rather specific to cyclobutanones and cyclobutenones. The remarkable selectivity and the excellent yields of such transformations, which are favored or caused by ring strain as the inherent driving force, offer the synthetic chemist fascinating possibilities for the development of new strategies for the synthesis of natural products and biologically active compounds.
    Additional Material: 2 Tab.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 1113-1126 
    ISSN: 0570-0833
    Keywords: Indoles ; Synthetic methods ; Transition metals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of transition-metal complexes as reagents for the synthesis of complex organic compounds has been under development for at least several decades, and many extraordinary organic transformations of profound potential have been realized. However, adoption of this chemistry by the practicing synthetic organic chemist has been inordinately slow, and only now are transition-metal reagents beginning to achieve their rightful place in the arsenal of organic synthesis. Several factors contributed to the initial reluctance of synthetic organic chemists to use organometallic reagents. Lacking education and experience in the ways of elements having d electrons, synthetic chemists viewed organometallic processes as something mysterious and unpredictable, and not to be discussed in polite society. Organometallic chemists did not help matters by advertising their latest advances as useful synthetic methodology, but restricting their studies to very simple organic systems lacking any serious functionality (e.g., the “methyl, ethyl, butyl, futile” syndrome). Happily, things have changed. Organometallic chemists have turned their attention to more complex systems, and more recently trained organic chemists have benefited from exposure to the application of transition metals. This combination has set the stage for major advances in the use of transition metals in the synthesis of complex organic compounds. This review deals with one aspect of this area, the use of transition metals in the synthesis of indoles.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 226-246 
    ISSN: 0570-0833
    Keywords: Zeolites ; Catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Zeolites have proved to be valuable technical catalysts in petrochemistry and in oil processing. The characteristic properties of zeolites, such as acidity, shape-selectivity and thermal stability also enable them to be used for highly selective synthesis in the fields of chemical intermediates and fine chemicals. This interesting area of application has grown continuously in recent years. The present article summarizes the various standard types of reaction involved in organic syntheses which can be catalyzed by zeolites; these include, inter alia, electrophilic and nucleophilic substitution reactions, isomerization of double bonds and carbon skeletons, as well as addition, elimination and hydrogenation reactions.
    Additional Material: 2 Ill.
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  • 10
    ISSN: 0570-0833
    Keywords: Ketenimines ; Carbene ligands ; Isocyanides ; Carbocycles ; Heterocycles ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ketenimine complexes are readily available in great variety by reaction of isocyanides with carbene complexes. They have proven to be useful building blocks in new synthetic approaches to carbocyclic and N-heterocyclic four-, five-, and six-membered rings. The reactions involve new metal-induced bond formation patterns of the ketenimine ligands, which can be influenced across a wide range by varying the following five parameters: the metal, the ligands, and the three substituents on the N=C=C unit.
    Additional Material: 8 Tab.
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  • 11
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 1484-1508 
    ISSN: 0570-0833
    Keywords: Phosphaalkynes ; Synthetic methods ; Phosphorus-carbon compounds ; Multiple bonds ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organophosphorus compounds have been applied in two ways in chemical synthesis. They can either be used as a reagent in a step of the synthesis (for example, in the Wittig reaction) or they can be incorporated directly into the target molecule. This second application, in particular, has expanded greatly in the last few years with the preparation of low-coordination phosphorus compounds. These include the phosphaalkynes, which are of great interest to organic and inorganic chemists. Phosphaalkynes have been employed in the synthesis of heterocyclic compounds, phosphaarenes and their valence isomers, and polycyclic compounds. Further applications have been the use of phosphaalkynes as new ligand systems in complex chemistry and their cyclooligomerization with organometallic reagents. While the chemical properties of phosphaalkynes have little in common with those of nitriles, they are in many ways very similar to those of the isoelectronic acetylenes.
    Additional Material: 4 Tab.
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  • 12
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 27 (1988), S. 622-642 
    ISSN: 0570-0833
    Keywords: Synthetic methods ; Enzyme catalysis ; Fermentation ; Biotechnology ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In recent years, the most significant development in the field of synthetic organic chemistry has been the application of biological systems to chemical reactions. Reactions catalyzed by enzymes and enzyme systems display far greater specificities than more conventional organic reactions. Biological and/or enzymatic syntheses and transformations, that is, “microbial transformations,” have great potential. Some of these reactions have already been shown to have useful applications in the fields of synthetic organic chemistry and biotechnology. This article reviews the current status of the rapidly developing field of microbial transformation, the methodology, available technological procedures, and fields of application being described especially in relation to conventional organic synthesis methods.
    Additional Material: 16 Ill.
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  • 13
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 15-23 
    ISSN: 0570-0833
    Keywords: Monosaccharides ; Synthetic methods ; Carbohydrates ; Heptoses ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The evolution of a strategy to synthesize the title compounds is described. Three principal developments allowed realization of this goal: (1) the attainment of high margins of diastereofacial selectivity and regioselectivity in the construction of pyranoid systems via the Lewis acid-catalyzed cyclocondensation reaction of activated dienes and aldehydes; (2) the exploitation of stereoselective reactions for functionalization of the pyranoid matrix; and (3) the discovery of stereoselective reactions for extending the chiral biases of pyranoid systems to newly emerging stereogenic centers on side chains. The coordination of these components in the synthesis of target systems of high biological interest is described.
    Additional Material: 18 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 190-203 
    ISSN: 0570-0833
    Keywords: Homogeneous hydrogenation ; Hydrogenation ; Synthetic methods ; Catalysis ; Stereoselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereochemical control is a major concern in the application of homogeneous catalysis to organic chemistry. In this context, the directed hydrogenation of olefins employing cationic rhodium or iridium catalysts has considerable potential, for very high selectivity can be attained under mild reaction conditions. The only requirement is a polar functional group in proximity to the double-bond which remains bound to the metal during the catalytic cycle and thereby controls the Stereochemical course of hydrogen delivery through the constraints of chelation. The substituent is most frequently a hydroxy group OH but can also be an ester, amide or carbamate group; other groups remain to be scrutinized. In cyclic compounds, directed hydrogenation can lead to face-selectivity, and the polar substituent may be in the β-, γ-, or δ-position to the double-bond. Acyclic stereoselection ensues with β- or γ-substituents in appropriate compounds, and the configuration of reduced product is predictable on the basis of simple rules. The application of optically active rhodium complexes leads to useful kinetic resolution procedures.
    Additional Material: 12 Ill.
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  • 15
    ISSN: 0570-0833
    Keywords: Glycopeptides ; Molecular recognition ; Molecular recognition ; Synthetic methods ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glycopeptides are partial structures of the connecting regions of glycoproteins and, like these, always contain glycosidic bonds between the carbohydrate and peptide parts. Glycoproteins are not only widely distributed but are also decisive factors in post-translational biological selectivity, especially in biological recognition. Targeted syntheses of glycopeptides require stereoselective formation of the glycosidic bonds between the carbohydrate and the peptide parts and protective group methods that enable selective deblocking of only one functional group in these polyfunctional molecules. These heavy demands have been met by the well-established use of benzylic protective groups, which can be removed by hydrogenolysis, combined with the use of base-labile 2-phosphonioethoxycarbonyl (Peoc) or 9-fluorenylmethoxycarbonyl (Fmoc) protective groups or of bromoethyl esters, which can be removed under neutral conditions. The acidolysis of tert-butyloxycarbonyl (Boc) groups and of tert-butyl esters has also been successfully used, although, under acidic conditions, anomerization or rupture of the glycosidic bonds may occur, especially when nucleophiles are present. The stable, two-stage 2-(pyridyl)ethoxycarbonyl (Pyoc) protective groups allow a more reliable synthesis of complex glycopeptides since they can be removed, after modifications, under mild conditions. Particularly suitable for the synthesis of sensitive glycopeptides are the stable allyl protective groups. They can be removed from the complex glycopeptides in a highly selective and effective manner by means of noble-metal catalysts under practically neutral conditions. These methods have been employed to synthesize glycopeptides corresponding to partial structures of interesting glycoproteins. Deprotected glyopeptides representing tumor-associated antigen structures can be coupled to bovine serum albumin, which serves as a biological carrier molecule, without the necessity of using an artificial coupling component (spacer).
    Type of Medium: Electronic Resource
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  • 16
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 24-37 
    ISSN: 0570-0833
    Keywords: Stereoselective aldol reactions ; Aldol reaction ; Chiral enolates ; Enolates ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aldol reaction is among the most important methods of forming carbon-carbon bonds. The addition of an enolate to an aldehyde leads to the formation of at least one chiral center. In the case of α-substituted enolates it has to a large extent been possible to control the product stereochemistry, while the aldol reaction of α-unsubstituted chiral enolates was for many years a “problem child” for synthetic chemists because of its insufficient stereoselectivity. Progress in this area has only been made in the last few years using either new chiral auxiliaries or alternatives to the aldol reaction.
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  • 17
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 204-217 
    ISSN: 0570-0833
    Keywords: Synthetic methods ; Reduction ; Carbanions ; Cycloannelation ; Cycloalkenes ; Polycycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The successive reduction of fully conjugated cyclic hydrocarbons leads to singly and multiply charged ions with unusual bonding. The charge distribution in these ions can be determined spectroscopically, and the information so obtained is then used in kinetically controlled trapping reactions for the regioselective introduction of electrophilic groups. When non-benzenoid substrates are used, syntheses become possible which can either not be carried out or can only be carried out with great difficulty in other ways. Examples of new preparative applications are cycloannelation and bridging reactions as well as polymerization reactions. The ion pair structure of the intermediate and the type of electrophile used are of paramount importance in controlling the mechanism of these reductive transformations.
    Additional Material: 4 Ill.
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  • 18
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 489-503 
    ISSN: 0570-0833
    Keywords: Natural products ; Synthetic methods ; Polyketides ; Stereoselectivity ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sequences of directly adjacent stereogenic centers were first discovered for the monosaccharides, which therefore constituted the first focus of interest in Stereoselective synthesis. The structures of many polyketide-derived natural products that have been elucidated in recent years often exhibit longer sequences of stereogenic centers in which hydroxy-substituted secondary carbon atoms alternate with tertiary carbon atoms. This finding inspired the development of methods allowing the specific construction of first two and then - more importantly-three neighboring stereogenic centers. The diverse methodologies that have thereby emerged reveal common principles and stress the variety of approaches possible in stereoselective synthesis.
    Additional Material: 2 Tab.
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  • 19
    ISSN: 0570-0833
    Keywords: Glycosides ; Oligosaccharides ; Koenigs-Knorr method ; Synthetic methods ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glycoproteins, glycolipids, and glycophospholipids (glycoconjugates) are components of membranes. The oligosaccharide residue is responsible for intercellular recognition and interaction; it acts as a receptor for proteins, hormones, and viruses and governs immune reactions. These significant activities have stimulated interest in oligosaccharides and glycoconjugates. With their help it should be possible to clarify the molecular basis of these phenomena and to derive new principles of physiological activity. Major advances in the synthesis of oligosaccharides have been made by the use of the Koenigs-Knorr method, in which glycosyl halides in the presence of heavy-metal salts are employed to transfer the glycosyl group to nucleophiles. The disadvantages of this procedure have led to an intensive search for new methods. Such methods will be discussed in this article. Emphasis is placed on glycoside and saccharide formation by 1-O-alkylation, on the trichloroacetimidate method, and on activation through the formation of glycosylsulfonium salts and glycosyl fluorides.
    Additional Material: 6 Ill.
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  • 20
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 414-430 
    ISSN: 0570-0833
    Keywords: Gas-phase flow thermolysis ; Thermolysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preference for carrying out synthetic organic reactions at the lowest possible temperature is due to the expectation that the selectivity often increases with decreasing temperature, as is confirmed by many examples and also theoretically justified. Selectivity, however, is not the only problem at high temperatures; further factors include the frequently limited thermal stability of the functional groups and structural elements not directly involved in the transformation. In spite of these limitations, the advantages of high temperatures and the greatly improved knowledge of the mechanisms of dynamic gas-phase processes accumulated in recent years can be exploited in directed organic synthesis. In this review the synthetic potential of gas-phase flow thermolysis will be described from the viewpoint of the synthetic chemist with the aid of typical examples of application.
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  • 21
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 508-524 
    ISSN: 0570-0833
    Keywords: Cross-coupling ; Organotin compounds ; Electrophilicity ; Palladium ; Catalysis ; C-C coupling ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cross-coupling of organotin reagents with a variety of organic electrophiles, catalyzed by palladium, provides a novel method for generating a carbon-carbon bond. Because this mild, versatile reaction is tolerant of a wide variety of functional groups on either coupling partner, is stereospecific and regioselective, and gives high yields of product, it is ideal for use in the synthesis of elaborate organic molecules. When the coupling reaction is carried out in the presence of carbon monoxide, instead of a direct coupling, carbon monoxide insertion takes place, stitching the two coupling partners together and generating a ketone.
    Additional Material: 1 Ill.
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  • 22
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 960-970 
    ISSN: 0570-0833
    Keywords: Phase-transfer catalysis ; Catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The development of Phase Transfer Catalysis (PTC) represents a major step forward in the employment of many organic reactions and renders them very convenient and useful processes. These reactions involve the application of nucleophiles in general, anions and bases in particular, in reactions carried out in a water-organic solvent system. They can be performed both in the laboratory and on an industrial scale. The ease of application of PTC processes is the main reason for their increasing utilization in industry. An outstanding achievement of this technique is the employment of aqueous bases in reactions which traditionally would otherwise require a strong base in a nonaqueous medium. The classical procedures that require severe anhydrous conditions, expensive solvents and dangerous bases such as metal hydrides and organometallic reagents are now replaced by aqueous solutions of, e.g., sodium or potassium hydroxides (PTC/OH processes). In contrast to the extensive synthetic applications of PTC/OH systems, the detailed mechanisms of these processes have been the subject of a great deal of controversy and various mechanisms have been suggested. However, it would seem that our knowledge concerning the mechanistic aspects of such reactions has now reached the stage where it can be used to advantage in synthesis planning. A better understanding of the various factors which influence the reaction would undoubtedly help to optimize PTC/OH processes such as to enable higher yields in shorter reaction times at lower temperatures. The importance of, inter alia, the catalyst will be pointed out and it is highly recommended that such catalysts be always available in the laboratory, for the range of organic reactions that they can efficiently, conveniently and safely catalyze is vast indeed.
    Additional Material: 5 Ill.
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  • 23
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 1-20 
    ISSN: 0570-0833
    Keywords: Cycloaddition ; Trimethylenemethane ; Synthetic methods ; Cyclopentanes ; Heterocycles ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The power of cycloadditions for ring formation derives from the potential for chemo-, regio-, diastereo-, and enantioselectivity. Trimethylenemethane (TMM) and its equivalents offer the possibility of extending such benefits to the synthesis of five-membered rings. Three types of conjunctive reagents appear to be promising candidates: (1) selected 4-alky-lidene-4,5-dihydro-3H-pyrazoles, (2) 2-[(trimethylsilyl)methyl]allyl esters and halides, and (3) alkylidenecyclopropanes. Thermal reactions, especially intramolecular ones, effect the cycloaddition of the pyrazoles to olefins-especially electron-poor olefins. The latter two precursors require a catalyst, notably a palladium complex, to unlock the synthetic potential. With the 2-[(trimethylsilyl)methyl]allyl esters, a general chemo-, regio-, and diastereoselective cycloaddition with typical Diels-Alder dienophiles forms methylenecyclopentanes in both inter- and intramolecular fashion. A tin analogue allows extension of this cycloaddition to aldehydes, and, in a related sequence, to ketones and imines to form 3-methylenete-trahydrofurans and 3-methylenepyrrolidines with excellent diastereoselectivity. The 2-[(tri-methylsilyl)methyl]allyl esters also serve to effect net methylenecyclopentane annulation to cyclic enols. Such adducts can further undergo three-carbon intercalation or combined ring contraction-spiroannulation simply by the use of either a nucleophilic or electrophilic trigger. Alkylidenecyclopropanes undergo cycloadditions to both electron-rich and electron-poor olefins when stimulated by metal catalysts, especially palladium. A complementary regiochemistry to the approach based upon silicon conjunctive reagents is observed. The availability of these cycloadditions provides new strategies for the synthesis of natural products.
    Additional Material: 2 Tab.
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  • 24
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 683-701 
    ISSN: 0570-0833
    Keywords: Electroorganic synthesis ; Electrochemistry ; Synthetic methods ; Redox chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical formation and regeneration of redox agents for organic syntheses (indirect electrolysis) widens the potential of electrochemistry, as higher or totally different selectivities can often be obtained while at the same time the energy input can be lowered significantly. Higher current densities can also be obtained by preventing otherwise often encountered electrode inhibition. New types of redox catalysts can be formed in-situ and can be regenerated after reaction with the substrates. This principle is of increasing importance also for the application of already known redox agents with regard to environmental protection, since large amounts of a product can be generated in a closed circuit using only relatively small amounts of the redox reagent. Consequently the operation of such a process can be greatly simplified, and the release of ecologically objectionable spent reagents into the environment can be prevented. The broad spectrum of redox catalysts currently in use includes, inter alia, metal salts in very low or high oxidation states, halogens in various oxidation states, and, in particular, a wide variety of transition-metal complexes. A great deal of progress has recently been made in the application of organic electron transfer agents, since compounds have been found that are sufficiently stable in both the reduced as well as the oxidized state.
    Additional Material: 3 Ill.
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  • 25
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 790-807 
    ISSN: 0570-0833
    Keywords: Anthracyclinones ; Synthetic methods ; Antibiotics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The remarkable antitumor properties of anthracycline antibiotics have motivated synthetic chemists, and a large number of groups have been active recently in this field. Initially, there was very little hope for this class of substances due to their extreme toxicity. However, the dividing line between toxicity and desired pharmacological effect has broadened to such an extent, partly through microbiological methods (new strains, mutants) and partly through semisynthetic modifications, that today anthracyclines take number one place (over 20% of the market) in the chemotherapy of (human) cancer. The demands made on modern cytostatica are extremely high, as may be seen from the fact that of the more than 600000 drugs tested in animals, only about 40 are in clinical use. In the meantime, some anthracyclines obtained by total synthesis are also in clinical testing. In this review it will hopefully be demonstrated that all those concerned in the chemotherapeutic use of these substances have also contributed to the general progress made in the solution of regio- and stereo-chemical problems of linearly annelated ring systems.
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  • 26
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 25 (1986), S. 947-959 
    ISSN: 0570-0833
    Keywords: Lewis acids ; Synthetic methods ; Selectivity ; Organocopper compounds ; Addition ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organometallic compounds with pronounced nucleophilicity such as organocopper and organolithium compounds, and powerful electrophiles, such as BF3 and AlCl3, are generally thought to be incompatible under normal, homogeneous reaction conditions. As a matter of course, it is anticipated that the two species cannot coexist and undergo transmetalation reactions. To our surprise, however, RCu and BF3 are compatible at low temperature. RCu·BF3 and related organocopper-Lewis acid reagents exhibit new and unique reactivities and selectivities: in conjugate additions, e.g., not only activation but also high regio-, stereo-, and chemo-selectivity as well as very high asymmetric induction is observed; allylic derivatives are alkylated regioselectively, and reaction towards carbonyl groups, imines, epoxides, aziridines, ethers, acetals, orthoformates, and pyridinium salts is in each case found to be selective. RLi·BF3 and related organolithium-Lewis acid reagents also exhibit noteworthy selectivities and reactivities. These complex reagents are utilized in the key steps of the total synthesis of many important natural products, such as certain terpenes, steroids, and alkaloids.
    Additional Material: 5 Tab.
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  • 27
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 24 (1985), S. 539-553 
    ISSN: 0570-0833
    Keywords: Chirality ; Reduction ; Synthetic methods ; Enzymes ; Biotechnology ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It has been known for many decades that chiral compounds can be obtained by stereospecific biocatalytic reduction. Further significant methodological developments in this field have, however, only been made during the past ten years; they include the application of previously unused microorganisms and electron donors, the discovery of additional substrates for the known reductases, the development of methods for regenerating reduced pyridine nucleotides, and the discovery of new reductases which were sought for specific preparative purposes. Many chiral compounds can now be synthesized by microbial hydrogenation using H2 and hydrogenase-containing microorganisms as well as by electromicrobial or electroenzymatic reduction. In the two latter methods, anaerobic or aerobic organisms are supplied with electrons from electrochemically reduced, artificial mediators, e.g., methyl viologen. Reductases that do not require pyridine nucleotides and can accept electrons directly from reduced viologens are especially useful. Two examples of this type of enzyme are described which are of preparative interest. Many cells contain methyl viologen-dependent NAD(P) reductases, a large number of which have still not been characterized. A productivity number is proposed which allows different methods of bioconversion with microorganisms to be compared. The productivity numbers of compounds synthesized by the methods described in this review are often 10- to 100-fold higher than those of substances obtained by conventional techniques.
    Additional Material: 7 Ill.
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  • 28
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    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 24 (1985), S. 553-565 
    ISSN: 0570-0833
    Keywords: Free radicals ; Organomercury compounds ; Synthetic methods ; Organotin compounds ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: C—C bond formation is one of the most important synthetic steps in the construction of organic molecules. In the last few years it has been increasingly achieved by radical addition to alkenes. In such reactions the adduct radicals have to be trapped by an donor subsequent to the C—C bond formation in order to prevent polymerization. This task can be accomplished with organotin and organomercury hydrides, the use of which has led to new synthetic methods. The occurrence of radical chain reactions in which reactions take place between radicals and nonradicals is decisive for the success of the synthesis. In these cases small amounts of radical initiators suffice and numerous functional groups may be used in the C—C bond-forming reactions. The yields and selectivities of these radical reactions are often very high.
    Additional Material: 1 Tab.
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  • 29
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    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 24 (1985), S. 617-638 
    ISSN: 0570-0833
    Keywords: Enzyme catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enzymes have great potential as catalysts for use in synthetic organic chemistry. Applications of enzymes in synthesis have so far been limited to a relatively small number of largescale hydrolytic processes used in industry, and to a large number of small-scale syntheses of materials used in analytical procedures and in research. Changes in the technology for production of enzymes (in part attributable to improved methods from classical microbiology, and in part to the promise of genetic engineering) and for their stabilization and manipulation now make these catalysts practical for wider use in large-scale synthetic organic chemistry. This paper reviews the status of the rapidly developing field of enzyme-catalyzed organic synthesis, and outlines both present opportunities and probable future developments in this field.
    Additional Material: 2 Ill.
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  • 30
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 24 (1985), S. 668-682 
    ISSN: 0570-0833
    Keywords: Organoaluminum compounds ; Synthetic methods ; Selectivity ; Beckmann rearrangement ; Rearrangement ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In addition to their high oxyphilicity, organoaluminum compounds are endowed with ambiphilic character. These properties can be successfully utilized in developing new synthetic reactions with unique selectivities. Especially noteworthy are the organoaluminum-promoted Beckmann rearrangement of oxime sulfonates, new syntheses of polyamino macrocycles via reductive cleavage of aminals and amidines by diisobutylaluminum hydride, the diastereoselective cleavage of chiral acetals by organoaluminum compounds leading to optically active secondary alcohols, allylic alcohols, and β-substituted carbonyl compounds, and biomimetic terpene syntheses. These and other examples, which illustrate the characteristics of organoaluminum chemistry, are used to demonstrate the distinct advantages of organoaluminum reagents in selective organic synthesis.
    Additional Material: 11 Tab.
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  • 31
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    Angewandte Chemie International Edition in English 18 (1979), S. 515-529 
    ISSN: 0570-0833
    Keywords: Pyrolysis ; Sulfones ; Synthetic methods ; Ring contraction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclic sulfoness containing structural elements such as aromtic rings, heteroatoms. functional groups, and further SO2-groups as ring members decompose on heating with cleavage of SO2 and formation of a new C—C bond. In the last decade this “sulfone pyrolysis” has been expanded into a generally applicable method even allowing the synthesis of sterically strianed medium-membered and multi-membered cyclic and polycyclic systems containing aromatic ring. By the pyrolysis of sulfones which are only unilateally activated by benzyl moieties, aromatic systms can be bridged by —(CH2)n chains of any desired length. In addition, —(CH2)— chains can be split off together with two SO2 molecules, with recombination of the remaining centers, resulting in ring contraction by four to n atoms. However, sulfone pyrolysis is of importance not only as a ring-contraction method but as a crucial final step in the synthesis of multi-membered hydrocarbon cycles, e.g. of the phane type.
    Additional Material: 7 Ill.
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  • 32
    ISSN: 0570-0833
    Keywords: Donor-acceptor systems ; Substituent effects ; Free radicals ; Radicophiles ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto-dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd-Substitution has synthetically useful applications: cd-substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross-conjugated cd-substituents are “radicophilic” and permit twofold carbon radical addition. cd-Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd-substituted molecules appear to involve radicals.
    Additional Material: 6 Ill.
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  • 33
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    Angewandte Chemie International Edition in English 18 (1979), S. 421-429 
    ISSN: 0570-0833
    Keywords: Triphase catalysis ; Catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Triphase catalysis (TC) has recently been introduced as a unique form of heterogeneous catalysis in which the catalyst and each of a pair of reactants are located in separate phases. Based on this concept, new synthetic methods have been developed for aqueous phase-organic phase reactions using a solid phase catalyst. Although it is only at an early stage of development, TC shows considerable potential for practical use. Our mechanistic understanding of these highly complex catalytic systems is at present very limited and detailed examination will be required before their relationship to phase-transfer, micellar, and interfacial catalysis becomes clear.
    Additional Material: 2 Ill.
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  • 34
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    Angewandte Chemie International Edition in English 18 (1979), S. 837-846 
    ISSN: 0570-0833
    Keywords: C-C coupling ; Synthetic methods ; Catalysis ; Silanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reagent hydrosilane/carbon monoxide opens up new possibilities for organic synthesis. Four cases will be discussed: 1. The reaction of olefins with hydrosilane (trialkylsilane) and carbon monoxide in the presence of Co, Ru, and Rh complexes leads to enol silyl ethers having one more carbon atom that the olefins. 2. Cyclic ethers underto carbonylative ring opening to ω-siloxyaldehydes when reacted with hydrosilane and carbon monoxide in the presence of Co2(CO)8 as catalysts 3. Aldehydes are catalytically converted into the next higher α-siloxyaldehydes or 1,2-bis(siloxy)alkenes depending on the reaction conditions used. 4. The reaction of alkyl acetates proceeds in various ways depending on the nature of the alkyl group; enol silyl ethers or alkenes are optained.-Mechanisms of these Co2(CO)8 catalyzed reactions using hydrosilane and carbon monoxide are discussed in which HCo(CO)n or R3SiCo(CO)nL function as catalytically active agents. With these species there are four types of catalytic cycles.-The synthetic possibilities of these catalytic reactions have still not been fully explored.
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  • 35
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    Angewandte Chemie International Edition in English 18 (1979), S. 900-917 
    ISSN: 0570-0833
    Keywords: Arylnitrene chemistry ; Synthetic methods ; Nitrenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Aryl- and heteroaryl-nitrenes can take part in intra-and intermolecular reactions in both of their possible electronic states (triplet and singlet). In this review we have endeavored to high-light recent synthetic uses of these reactive intermediates as well as draw attention to avenues open to further exploration in this field. Singlet arylnitrenes will interact with suitable ortho-positioned substituents to give a variety of fused azoles, some in excellent yield. In suitable solvents and in presence of amines and alcohols, phenylnitrenes undergo ring expansion to azepines which can also occur in nitrenes of certain fused bicyclic aromatics (naphthalene, quinoline, isoquinoline, benzo[b]thiophene). The latter nitrenes may also give rise to o-diamines which are useful starters for further heterocyclic synthesis. Triplet arylnitrenes (usually regarded as having only a nuisance effect in synthetic work) may also be utilized in practicable heterocyclic syntheses within a suitable molecular framework. Decomposition of aryl azides in a mixture of an organic and polyphosphoric acid leads to fused oxazoles. The mechanism is discussed for all the reactions considered.
    Additional Material: 8 Tab.
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  • 36
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    Angewandte Chemie International Edition in English 18 (1979), S. 707-721 
    ISSN: 0570-0833
    Keywords: Onium compounds ; Aza-arenes ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Effective syntheses employing 2-halogenated pyridinium, benzoxazolium, benzothiazolium, and pyridinium salts have been accomplished in the absence of strong acids and bases. Activation of carboxylic acids or alcohols with these onium salts leads to 2-acyloxy and 2-alkoxy intermediates which can be transformed into esters, amides, thiol esters, (macrocyclic) lactones, acid fluorides, olefins, allenes, carbodiimides isocyanates, isothiocyanates, nitriles, and isocyanates. The possibility of performing stereospecific syntheses (involving configurational inversion) with onium salts deserves attention.
    Additional Material: 20 Tab.
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  • 37
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    Angewandte Chemie International Edition in English 17 (1978), S. 476-486 
    ISSN: 0570-0833
    Keywords: Intramolecular reactions ; Ene reaction ; Synthetic methods ; Cyclization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermal cyclizations of appropriate dienes, enynes and related unsaturated systems, some of them carried out on an industrial scale, demonstrate increasingly the preparative power of the intramolecular ene reaction. A variety of substituted, fused and bridged ring systems, including natural products, are thus easily accessible in a regio- and stereo-selective manner. Numerous examples are discussed systematically illustrating the possibilities, limitations, and common features of this cyclization reaction and its reverse ring-opening process.
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  • 38
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    Angewandte Chemie International Edition in English 17 (1978), S. 27-37 
    ISSN: 0570-0833
    Keywords: Organomercury compounds ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organomercurials have been known since 1850 and many synthetic routes to these compounds presently exist. The ability of these compounds to accommodate a wide variety of functional groups and to tolerate quite diverse reaction conditions makes them attractive as synthetic intermediates. While the solvomercuration-demercuration and divalent carbon transfer reactions remain the most widely used of the organomercurial reactions, a number of new synthetic procedures employing organomercurials have been developed in recent years. Many of these involve transmetallation reactions with palladium salts.
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  • 39
    ISSN: 0570-0833
    Keywords: Oxygenation ; Alkanes ; Synthetic methods ; Superacidic systems ; Catalysis ; Magic acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Owing to the ready availability of the starting materials, the functionalization of saturated hydrocarbons for preparing chemical intermediates and products represents an attractive goal. The possibility of converting alkane in a controlled way into alcohols, ketones etc., i.e. to oxyfunctionalize them, is particularly challenging. After a short account of previous methods used for the oxidation of alkanes, particular emphasis will be given to recently developed reactions of alkanes with oxygenating agents in superacidic media.
    Additional Material: 16 Tab.
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  • 40
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    Angewandte Chemie International Edition in English 17 (1978), S. 169-175 
    ISSN: 0570-0833
    Keywords: Organoaluminum compounds ; Selectivity ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: With the aid of selected examples an overview is given of the development trends in highly discriminative reactions using organoaluminum compounds. (1) Isomerization of substituted oxiranes into allyl alcohols has been effected both stereo- and regioselectively by means of a new organoaluminum reagent, diethylaluminum 2,2,6,6-tetramethylpiperidide (DATMP); this reaction which provides a new route for the regiospecific transformation of allyl alcohols into 1,3-dienes. (2) A novel nonenzymic heterolysis of allylic phosphates of terpenoids has been effected by organoaluminum compounds and has enabled development of a new method for the selective synthesis of cyclic terpenes. (3) The reductive condensation of α-haloketones with carbonyl compounds in the presence of diethylaluminum chloride and zinc affords β-hydroxy-carbonyl derivatives in good yields with exclusion of undesired self-condensations products.
    Additional Material: 3 Ill.
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  • 41
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    Angewandte Chemie International Edition in English 17 (1978), S. 487-496 
    ISSN: 0570-0833
    Keywords: Alumina surfaces ; Synthetic methods ; Surface chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recent examples are given to emphasize that alumina can cause many different and often unexpected chemical reactions of adsorbed organic molecules. Recent developments are summarized to publicize that reagent-doped alumina can be used deliberately to achieve some very mild and highly selective organic transformations. The scope and limitations of organic reactions at alumina surfaces are discussed, and the advantages of these heterogeneous reactions over the corresponding homogeneous ones are pointed out. The role of the alumina and future problems are discussed briefly.
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  • 42
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    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 17 (1978), S. 505-515 
    ISSN: 0570-0833
    Keywords: Pyridines ; Alkynes ; Nitriles ; Synthetic methods ; Cobalt catalysts ; Catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Soluble organocobalt catalysts permit selective formation of substituted pyridines under mild conditions in a single step: mono-, di-, and trisubstituted pyridines can be obtained at will in high conversions and high yields from nitriles and alkynes. Polynuclear derivatives such as bipyridines can also be prepared by this method.
    Additional Material: 1 Ill.
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  • 43
    ISSN: 0570-0833
    Keywords: 4-Dialkylaminopyridines ; Amino pyridines ; Acylation ; Catalysis ; Synthetic methods ; Pyridines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 4-dialkylaminopyridines can be accomplished in two steps starting from pyridine. Compared to pyridine, these derivatives are approximately 104 times more active when used as acylation catalysts. Dialkylaminopyridines are being used with ever-increasing frequency for acylation reactions which proceed either incompletely or not at all in pyridine. This article reviews the various possible applications of 4-dialkylaminopyridines in terpene, steroid, carbohydrate and nucleoside chemistry as well as in the transformation of amino acids into α-acyl aminoketones and polymerization of isocyanates. In addition, N-substituted 4-dialkylaminopyridinium salts can be used for the transfer of sensitive groups to nucleophiles in aqueous medium. The exceptional catalytic effect of these derivatives, even in non-polar solvents, is due, in part, to the formation of high concentrations of N-acylpyridinium salts which are present in solution as loosely-bound, highly reactive ion pairs.
    Additional Material: 2 Ill.
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  • 44
    ISSN: 0570-0833
    Keywords: Phosphorus ylides ; Ylides ; Phosphorus ylides ; Synthetic methods ; Phosphorus ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phosphacumulene ylides and phosphaallene ylides are nucleophilic compounds which can add reactants in a variety of ways. Cycloadditions can occur both at the polar C - P ylide bond and at the C=C double bond.
    Additional Material: 13 Tab.
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  • 45
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    Angewandte Chemie International Edition in English 16 (1977), S. 365-373 
    ISSN: 0570-0833
    Keywords: Flash thermolysis ; Thermolysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Flash thermolysis is a special form of gas-phase thermolysis that is particularly suitable for the production and isolation of thermolabile reaction products. The theoretical basis and the instrumental requirements of the method are first given, and the preparative importance of flash thermolysis for the synthesis of thioketenes, allenes, arynes, highly strained ring systems, quinodimethanes, and other reactive compounds is then demonstrated with the aid of examples.
    Additional Material: 2 Ill.
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  • 46
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    Angewandte Chemie International Edition in English 16 (1977), S. 339-348 
    ISSN: 0570-0833
    Keywords: α-Metalated isocyanides ; Isocyanides ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Being both nucleophilic and electrophilic, α-metalated isocyanides can add to polar double bonds, forming heterocycles. They are also synthons for α-metalated primary amines. This article describes recent or improved procedures for their use in organic synthesis: (1) In heterocyclic syntheses to give 2-oxazolines, 2-imidazolines, 2-thiazolines, oxazoles and oligooxazoles, thiazoles, triazoles, imidazolinones, pyrroles, 5,6-dihydro-1,3-oxazines and -thiazines, and (via cycloaddition with nitrones) 2-imidazolidinones. (2) In the field of formylaminomethylenation, for example transformation of estrone methyl ether and a keto sugar into the corresponding α-formylaminoacrylic esters, and the conversion of aldehydes and ketones by 3- and 4-pyridyl-methyl isocyanides into N-(1-pyridyl-1-alkenyl)formamides and their hydrolysis to 3- and 4-acylpyridines. (3) In connection with the use of α-metalated isocyanides as synthons for α-metalated primary amines, the author demonstrates how they may be used for preparation of 1,2- and 1,3-amino alcohols, 1,2-diamines, 2,3-diaminoalkanoic acids and for synthesis of higher amino acids starting from simple amino acids.
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  • 47
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    Angewandte Chemie International Edition in English 16 (1977), S. 493-505 
    ISSN: 0570-0833
    Keywords: Phase-transfer catalysis ; Catalysis ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phase-transfer catalysis (PTC) has grown into a versatile preparative method in the last few years. The most notable new developments include the use of crown ethers as phase-transfer catalysts and the introduction of solid-liquid PTC. Some representative examples have been selected from the large number of new PTC reactions and some of them are summarized in tables.
    Additional Material: 11 Tab.
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  • 48
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 16 (1977), S. 817-826 
    ISSN: 0570-0833
    Keywords: Titanium tetrachloride ; Synthetic methods ; Catalysis ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Titanium tetrachloride can accelerate numerous organic reactions. Valuable syntheses of, e.g., allyl sulfides, amides, enamines, and ketones are based upon transformations of functional groups with TiCl4. Particular mention should also be made of carbon-carbon linkage with TiCl4 which permits the synthesis of hydroxy ketones and carbonyl compounds of the Michael adduct type. TiCl4 reduced in situ is suitable for the reduction of chloroarenes or the linkage of two aldehyde molecules to give an alkene.
    Additional Material: 7 Tab.
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  • 49
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 16 (1977), S. 10-23 
    ISSN: 0570-0833
    Keywords: Cycloaddition ; Synthetic methods ; Intramolecular reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Numerous examples of intramolecular cycloaddition of 1,3-dienes, nitrones, and azomethine imines attest the preparative value of this variant for regioselective and stereoselective synthesis of annelated and bridged ring systems. The common features, differences, and limitations of these types of reaction are systematically reviewed.
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  • 50
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 15 (1976), S. 1-9 
    ISSN: 0570-0833
    Keywords: Betaines ; Synthetic methods ; Cycloaddition ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cycloadditions of 3-hydroxy-1-methylpyridinium betaines with electron-deficient olefins have been extended to a variety of 1-substituents in place of methyl. Application of resonance theory and later of quantum chemical methods led to rationalization of preceding results and prediction of new reactions. Thermal additions of 2π- and 6π-electron addends at the 2,6-positions and of 4π-electron addends at the 2,4-positions are described. The cycloadducts are highly interesting potential synthetic building blocks.
    Additional Material: 1 Ill.
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  • 51
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 15 (1976), S. 333-340 
    ISSN: 0570-0833
    Keywords: Hydrozirconation ; Synthetic methods ; Zirconium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrozirconation has recently been developed as a procedure for functionalizing alkenes, alkynes, and 1,3-dienes via organozirconium(IV) intermediates. These intermediates react with a variety of electrophilic reagents to give organic products in high yield. Mechanisms of reactions involved in these sequences are discussed.
    Additional Material: 1 Ill.
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  • 52
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 15 (1976), S. 639-647 
    ISSN: 0570-0833
    Keywords: Addition ; Aldehydes ; Synthetic methods ; Esters ; Ketones ; Nitriles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the presence of cyanide ions as catalyst, aromatic and heterocyclic aldehydes can be smoothly added to α,β-unsaturated ketones, esters, and nitriles in aprotic solvents to form γ-diketones, 4-oxo carboxylic esters, and 4-oxo nitriles. Thiazolium salts in the presence of bases are also suitable catalysts; they permit not only addition of aromatic and heterocyclic aldehydes but also the addition of aliphatic aldehydes.
    Additional Material: 9 Tab.
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  • 53
    ISSN: 0570-0833
    Keywords: Synthetic methods ; Dihydrooxazoles ; Oxazoles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The oxazoline ring system, first prepared in 1884, has only in the last five years been shown to possess considerable utility in the synthesis of a variety of functionalized organic compounds. By appropriate metalation of the 2-alkyl substituent it is possible to prepare a variety of homologated carboxylic acid derivatives, both chiral and achiral. Various other manipulations of the oxazoline ring lead to aldehydes, ketones, lactones, amino acids, thiiranes, and olefins. Due to the inertness of the oxazoline ring system to various reagents (RMgX, LiAlH4, CrO3, mild acid or alkali) it may be utilized as a protecting group for carboxylic acids during the transformations involving the above reagents. Two major new developments in oxazoline chemistry involve (a) the use of a chiral oxazoline as a reagent for asymmetric synthesis of chiral carboxylic acids, lactones, alcohol, thiiranes, and olefins and (b) a new mode of aromatic substitution in which the aryloxazolines act as nucleophilic or electrophilic reagents. This behavior has led to a variety of polysubstituted benzenes and biphenyls which would be inaccessible by classical routes. A variety of examples illustrating the utility of oxazolines indicated above are presented so that the reader may appreciate the vast potential of this simple ring system in synthesis.
    Additional Material: 15 Tab.
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  • 54
    ISSN: 0570-0833
    Keywords: Halomalondialdehydes ; Malondialdehydes ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The present progress report provides a survey of the synthesis, structure, and reactions of halomalondialdehydes, including “cyanomalondialdehyde” (diformylacetonitrile), the only pseudohalogen compound so far known in this series. Halomalondialdehydes are reactive compounds, applicable in a variety of ways, and are characterized particularly by their cyclizations with bifunctional compounds. Many of the reactions discussed below can be applied to substituted malondialdehydes other than those specified.
    Additional Material: 1 Ill.
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  • 55
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 14 (1975), S. 734-745 
    ISSN: 0570-0833
    Keywords: Substitution ; Radical ions ; Intermediates ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new type of substition process at a saturated carbon atom is described. These reactions, which proceed via a chain sequence in which radical anions and free radicals are intermediates, are noteworthy for providing novel and powerful means of synthesis: they occur readily under mild conditions, they give excellent yields of pure products, and, in contrast to SN2 displacements, they are rather insensitive to steric hindrance. As a consequence, radical anion processes are especially valuable for the preparation of highly branched structures. Many inorganic and organic anions readily enter into these displacements and, indeed, amines are also effective. Systems which undergo substitutions via this electron transfer mechanism include benzylic, cumylic, strictly aliphatic, and heterocyclic molecules. It is of interest that a number of groups which do not behave as leaving groups in SN2 displacements are readily displaced at room temperature from a satureted carbon atom via the radical anion-free radical pathway, e.g., nitro, azide, sulfone, and ether groups.
    Additional Material: 3 Tab.
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  • 56
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 14 (1975), S. 222-231 
    ISSN: 0570-0833
    Keywords: Phosphorylcarbenes ; Carbenes ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phosphorylcarbenes, which have become known only recently during synthetic experiments in the field of phosphoryldiazoalkanes, have twofold preparative value. In the first place, they can be used to introduce phosphoryl groups into organic compounds, as in the phosphoryl-cyclopropanation of alkenes or arenes and in the phosphorylcyclopropenation of alkynes. Secondly, phosphorylcarbenes readily undergo rearrangements; hydride, alkyl, aryl, or acyl shifts lead to phosphorylated alkenes. The phosphorylcarbene/methylenephosphane oxide rearrangement provides access to the short-lived P analogs of the ketenes. Finally, the vinylcarbene/allene rearrangement was first discovered in this connection; it competes with ring closure to the cyclopropene.
    Additional Material: 11 Tab.
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  • 57
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 14 (1975), S. 473-485 
    ISSN: 0570-0833
    Keywords: Ring contraction ; Cyclobutanes ; Cyclopropylmethyl compounds ; Ring expansion ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclobutanes and cyclopropylmethyl compounds vicinally disubstituted in appropriate manner by one electron-donating group and one leaving or electron-receiving group undergo extremely facile ring contractions and expansions respectively. Unlike many rearrangements of small-ring compounds and most rearrangements of larger-ring compounds, these reactions usually give a single product in high yield and thus possess real synthetic interest. The subject matter of this progress report is classified according to the substituents in question since the nature of these groups largely determines the conditions under which rearrangement takes place.
    Additional Material: 2 Tab.
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  • 58
    ISSN: 0570-0833
    Keywords: Umpolung ; Nitrosamines ; Amines ; Synthetic methods ; Nucleophilic reactions ; Aminoalkylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: There are basically two kinds of hetero atoms in organic molecules: one kind confers electrophilic character upon the carbon atom to which it is bound, and the other kind turns it into a nucleophilic site. The development of methods permitting transitions between the two resulting categories of reagents has become an important task of modern organic synthesis. The scope of such umpolung of the reactivity of functional groups is discussed for the case of amines as an example. A method of preparing masked α-secondary amino carbanions consists in nitrosation of the secondary amine, followed by metalation of the resulting nitrosamine α-to the nitrogen, reaction with electrophiles, and subsequent denitrosation. Many examples are given for each of these steps which illustrate the wide scope of the overall synthetic operation (electrophilic substitution at the α-C atom of the secondary amine). Preliminary applications and a method for avoiding the handling of nitrosamines are presented, and the report concludes with a brief account of the significance of nitrosamines in the study of carcinogenesis and mutagenesis.
    Additional Material: 1 Ill.
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  • 59
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 14 (1975), S. 801-811 
    ISSN: 0570-0833
    Keywords: Tetrachloromethane ; Phosphanes ; Chlorination ; Dehydration ; Synthetic methods ; Phosphorus-nitrogen compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this review the processes occurring on the treatment of triphenylphosphane with tetrachloromethane are first reported; a key role is played here by (trichloromethyl)phosphonium chloride which reacts with a further amount of the phosphane to give the stable salt [chloro(triphenylphos-phoranediyl)methyl]triphenylphosphonium chloride by way of dichlorophosphorane and (dichloromethylene)phosphorane that is detectable only as an intermediate. The preparative application of the two-component system as a chlorinating, dehydrating, and P - N-linking reagent is ascribable to “phosphorylation”Here and below, “phosphorylation” is used lo mean in general the formation of a phosphorus derivative. In the narrower sense this term denotes the introduction of phosphoryl groups P(O). of the substrate in question through several reactive species. In these applications the reactions with the substrate compete with reactions of the two-component system with itself, so that the overall course of the reaction is in nearly all cases much more complex than was previously assumed. Nevertheless. very good results can be achieved by the use of this reagent, high yields and mild reaction conditions being characteristic.
    Additional Material: 1 Tab.
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  • 60
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    Electronic Resource
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    Angewandte Chemie International Edition in English 14 (1975), S. 528-538 
    ISSN: 0570-0833
    Keywords: Bredt rule ; Bridgehead alkenes ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: During the past eight years, bridgehead olefins have attracted rapidly increasing attention. In view of their significance with regard to the stereochemistry of alkenes, the study of certain reaction mechanisms, and the nature of the double bond, detailed research into this structural type appears highly desirable. Bridgehead olefins represent connective linkages between olefins in the ground state and species which can arise in the deactivation of photochemically excited alkenes and cycloalkenes and also contribute to our understanding of the structural conditions prevailing during cis-trans isomerization of alkenes.
    Additional Material: 2 Ill.
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  • 61
    ISSN: 0570-0833
    Keywords: Quinones ; Quinones ; Michael addition ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: If catechol or other hydroquinones are dehydrogenated in the presence of a nucleophilic reagent, the latter reacts, usually by Michael addition, with the quinone formed in situ. The wide range of possible variations offered by this synthetic method is comprehensively described in the present paper. procedures are given for carrying out typical reactions.
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  • 62
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 250-260 
    ISSN: 0570-0833
    Keywords: Unsaturated fatty acids ; Fatty acids ; Carbonyl olefination ; Synthetic methods ; Wittig reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It is shown that carbonyl olefination, i.e. the reaction of carbonyl compounds with alkylidene phosphoranes, can be sterically controlled. In some cases cis-olefins can be obtained by proper choice of the reaction conditions; trans-olefins are formed only in the presence of suitable structural factors. These cis-and trans-olefination reactions have opened new, stereo-specific routes to unsaturated and polyunsaturated fatty acids with differing positions and sequences of cis- and trans-double bonds and to ω-hydroxy and branched chain fatty acids.
    Additional Material: 2 Tab.
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  • 63
    ISSN: 0570-0833
    Keywords: Cyclization ; Dialdehydes ; Nitromethane ; Carbohydrates ; Polyalcohols ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Condensation of nitromethane with suitable diadehydes in alkaline medium provides a general method of cyclization, in which the methyl group of the nitromethane is incorporated into the ring. This method leads to 5-, 6-, and 7-membered rings and is equally applicable to aliphatic, aromatic, and sugar dialdehydes. For example, glyoxal is converted into 1,4-dideoxy-1,4-dinitro-neo-inositol, and glutaraldehyde into trans-2-nitrocyclohexane-1,3-diol, while the corresponding cyclization of xylo-trihydroxyglutaraldehyde leads to deoxy-nitroinositols having the scyllo, myo-1, and muco-3 configurations.-In the case of aromatic dialdehydes, the cyclization is accompanied by elimination of water. Thus, phthalaldehyde, naphthalene-2,3-dicarboxaldehyde, and homophthalaldehyde yield, respectively, 2-nitroindenol, 2-nitrobenzindenol, and 2-nitronaphthalene. -Application of the method to sugar dialdehydes (aldehydic diglycol derivatives of monosaccharides formed by periodate oxidation) constitutes an excellent synthesis of 3-amino sugars, since 3-deoxy-3-nitropyranoses are formed smoothly on cyclization, and the corresponding 3-amino derivatives are obtained by hydrogenation. Thus, the reaction sequence: periodate oxidation → cyclization with nitromethane → hydrogenation, leads in the case of α-and β-D-pentosides to 3-amino-3-deoxy-D-and-L-pentosides, respectively, with ribo, xylo, and arabino configurations. α-D-hexosides give derivatives with gluco, manno, and galacto configurations. 3-Amino-3,6-dideoxyglucosides of the D-and L-series are obtained from 6-deoxy-D-or-L-hexosides, respectively, and 3-aminohexosans with gulo, ido, and altro configurations are obtained from 1,6-anhydro sugars. Cyclization of the dialdehydes obtained from sedoheptulose and methyl 4,6-O-ethylidene-α-D-glucoside by periodate oxidation, leads to 3-nitro and, after hydrogenation, to 3-amino derivatives of 3-deoxyheptopyranoses.
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  • 64
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 24-29 
    ISSN: 0570-0833
    Keywords: 3-Aminoquinazol-4-one ; 3-Aminobenzotriazin-4-one ; Quinazolones ; Benzotriazinones ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Among the derivatives of 3-aminoquinazol-4-one and 3-aminobenzotriazin-4-one are compounds with narcotic, sedative, analgetic, and muscle-relaxant properties. Of special interest are compounds with one or several urethane groups and those substituted in the 3-position by a morpholine moiety.
    Additional Material: 4 Tab.
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  • 65
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 225-238 
    ISSN: 0570-0833
    Keywords: Pyridinium salts ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This review discusses syntheses leading to a new type of N-vinylpyridinium salts, to novel anionocyanines, to aminophenazines and alloxazines, as well as to (aza-) dehydroquinolizinium, acridizinium, and morphanthridizinium salts. In addition, Mannich reactions and aminoalkylations at active methylene groups of cycloimmonium salts, and their reactions with amines are treated. The possibilities offered by the “Ortoleva-King” reaction are demonstrated using numerous examples, such as a new route leading to the yohimbine skeleton.
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  • 66
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    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 309-323 
    ISSN: 0570-0833
    Keywords: s-Triazines ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation and properties of s-triazine are discussed. Nucleophilic reagents (even water) readily attack s-triazine. Thus, open-chain and heterocyclic compounds, e.g. formamidines, aminomethylene compounds, and triazole, pyridine, and pyrimidine deravatives are accessible from s-triazine. With amidines and imido ethers substituted triazines are obtained (by trans-triazination).The latter are formed via open-chain intermediates.
    Additional Material: 11 Tab.
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  • 67
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 2 (1963), S. 380-393 
    ISSN: 0570-0833
    Keywords: Pyridinium salts ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cleavage of N-phenylpyridinium or N-vinylpyridinium salts with secondary aliphatic amines leads to aromatic amino compounds or enamines which are often unobtainable by other routes. The other fragment, glutacondialdehyde or its monoanil, gives azulenes, as shown by Ziegler and Hafner, as well as König; these compounds can also be prepared from alkylpyridinium salts with cyclopentadienylsodium (Hafner). Syntheses of labile aldehydes which are otherwise difficult to obtain and of α-ketocarboxylic acids, starting from pyridinium salts and proceeding via nitrones or α-cyanoanils, are illustrated by many new examples. Benzimidazoles, benzothiazoles, and amidines are accessible from pyridinium salts via nitrones or α-cyanoanils; cyanoanils can be transformed into quinoxalines (including xanthopterine), perimidines, etc. Furthermore, nitrosonaphthols and nitrosonaphthylamines react with pyridinium salts containing an active methylene group on the nitrogen, leading to new ring systems. Further synthetic possibilities arise from nucleophilic displacements of the pyridine in pyridinium salts by SN 2 reactions. Combination of the route via nitrones with the methods of Arndt-Eistert, Ortoleva-King, or with chloromethylation constitutes a significant enlargement of its range of application. The formation of α-cyanoanils from diazoketones permits synthesis of α-keto-β-amino acids from α-amino acids, or of phenylglyoxylic acids from benzoic acids by chain extension.
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  • 68
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    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 1 (1962), S. 8-21 
    ISSN: 0570-0833
    Keywords: Addition ; Immonium ions ; Isocyanides ; Amino acids ; Synthetic methods ; Alkylidene ammonium ions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The α-addition of immonium ions and anions (OH-, SeH-, S2O3 2-, N3- NCO- NCS-, R—CO2 -, RO—CO2-) to isonitriles, accompanied by secondary reactions provides a means for the one-stage synthesis of organic nitrogen compounds starting with two to five different components. Thus, by the condensations of amines (ammonia, primary, and secondary aliphatic and aromatic amines, hydrazines) and aldehydes or ketones with isonitriles and acids, a number of α-aminocarboxylic acid amides, thioamides, selenoamides, 1,5-disubstituted retrazoles, hydantoin imides, thiohydantoin imides, α-acylamino carboxylic acid amides, oligopeptide derivatives, β-lactams, derivatives of penicillanic acid, urethanes, diacylimides, and various hydrazine derivatives, can be prepared. The reactions are easily carried out and take place under mild conditions. Yields of more than 90% are frequently encountered.
    Additional Material: 4 Tab.
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  • 69
    ISSN: 0570-0833
    Keywords: Amides ; Azolides ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 70
    ISSN: 0570-0833
    Keywords: Michael addition ; Pyridinium salts ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By Michael addition of the active methylene groups in pyridinium salts onto suitable acceptor compounds, α-pyridones, substituted pyridines, particularly pyridinecarboxylic acids and pyridylpyridines, including the minor alkaloid of tobacco nicotelline and annelized pyridines, can be prepared by a simple procedure and generally in good yields. From the Michael adducts, polycyclic aromatic hydrocarbons, e.g. substituted fluoranthenes and “bisfluoranthenes” can be prepared; internal Michael addition leads to pyrrolinopyrdinium salts. For example, Michael addition of pyridinium salts onto quinones gives phenacyl substituted quinones, from which benzofurans and cinnolines can be readily obtained.
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