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  • Electronic Resource  (6)
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  • 2010-2014
  • 1980-1984  (6)
  • 1960-1964
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  • 1870-1879
  • 1983  (6)
  • Heterocycles
  • Synthetic methods
  • 1
    Electronic Resource
    Electronic Resource
    Darstellung und Struktur von Pyrazolyl-Kationen mit Polymethin- und Methan-Gerüst (1983)
    Springer
    Monatshefte für Chemie 114 (1983), S. 219-225 
    Details
    ISSN: 1434-4475
    Keywords: Cyanine dyes ; Dipyrazolylmethanes ; Heterocycles ; N-15-NMR ; O-17-NMR ; Phenazon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The 4-pyrazoline-3-one1 reacts with 4-dimethylaminobenzaldehyde to yield the stable asymmetric cyanine dye2b which reacts with1 to give the colorless (aryl) (dipyrazolyl) methane3b. Using aldehydes with less cationstabilizing groups the polymethines2 are not isolated but only the methanes3. The structures of2b and3 are discussed by1 H,13C and Hetero NMR spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00798325
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  • 2
    Electronic Resource
    Electronic Resource
    Triazolo[4′,3′:4,5] [1,3,4]thiadiazolo[2,3-b]quinazolin-6-one (1983)
    Springer
    Monatshefte für Chemie 114 (1983), S. 339-342 
    Details
    ISSN: 1434-4475
    Keywords: Heterocycles ; Infrared ; 1H-NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung 3-Methyl-6H-[1,2,4]triazolo[4′ ,3′ : 4,5] [1,3,4]thiadiazolo[2,3-b]chinazolin-6-on (6) wurde mittels Kondensation von Isatoesäureanhydrid (1) mit 4-Amino-5-mercapto-3-methyl[1,2,4]triazol (2) und anschließender Cyclisierung von Zwischenverbindung3 mit POCl3 und PCl3 dargestellt. Als Alternative konnte6 auch über die Kondensation von 3-Amino-2-mercapto-3H-chinazolin-4-on (7) mitN-Carbethoxyhydrazin in Gegenwart von HCl und anschließender Cyclisierung der Zwischenverbindung8 mit Essigsäure synthetisiert werden. Die Strukturen der Verbindungen wurden mittels IR,1H-NMR und Mikroanalyse nachgewiesen.
    Notes: Abstract 3-Methyl-6H-[1,2,4]triazolo[4′,3′: 4,5] [1,3,4]thiadiazolo[2,3-b]quinazolin-6-one (6) has been synthesized by the condensation of isatoic anhydride (1) with 4-amino-5-mercapto-3-methyl-[1,2,4]triazole (2) and final cyclisation of the intermediate3 with POCl3 and PCl3. Alternatively6 could also be synthesized by the condensation of 3-amino-2-mercapto-3H-quinazolin-4-one (7) withN-carbethoxy hydrazine in presence of hydrochloric acid and final cyclisation of the intermediate8 with acetic acid. The structures have been confirmed on the basis of IR, PMR and analytical results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00798956
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  • 3
    Electronic Resource
    Electronic Resource
    Organometallic Compounds of Titanium and Zirconium as Selective Nucleophilic Reagents in Organic SynthesisTaken in part from the Dissertation of B. Weidmann, ETH Zürich (1982), Diss. No. 7203. (1983)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 22 (1983), S. 31-45 
    Details
    ISSN: 0570-0833
    Keywords: Nucleophilic reactions ; Synthetic methods ; Selectivity ; Organotitanium compounds ; Organozirconium compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The addition of carbanionic organometallic compounds (usually RLi or RMgX) to a carbonyl group - a key step in numerous syntheses - is not always straightforward. Depending on the substrate, various complications and problems may arise, but in many cases these can be remedied by addition of (RO)3TiCl, (RO)3ZrCl or (R2N)3TiX to the classic lithium and Grignard reagents. This usually leads to formation of stable organo-titanium and -zirconium compounds which react highly selectively with carbonyl groups. For example, CH3Ti(OiPr)3 reacts five orders of magnitude faster with benzaldehyde than with acetophenone at room temperature; reagents of the type RTi(OiPr)3 add smoothly to nitro-, ido-, or cyano-subsituted benzaldehyde, and the reactions may be performed in chlorinated solvents or acetonitrile; the zirconium analogues have particularly low basicity and add in high yield to α- and β-tetralones or to substrates containing a nitroaldol group; the inclusion of chiral OR* groups gives enantioselective reagents (up to 90% ee); allylic (RO3)Ti- derivatives react only at the more highly substituted carbon atom and, in addition, react diastereoselectively (up to 98% ds) with unsymmetrical ketones. Finally, titanium reagents have also been found to effect novel transformations such as direct geminal dialkylation (C=O→CMe2) and alkylative amination [C=O→CR(NR2′)]. The modification and finetuning (“taming”) of carbonyl reactivity obtainable by use of the new reagents is not dearly bought; starting materials are the cheap and harmless “titanates”, “zirconates” and the corresponding tetrachlorides.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198300311
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  • 4
    Electronic Resource
    Electronic Resource
    The Versatile Chemistry of 1,4-Diazines: Organic, Inorganic and Biochemical Aspects (1983)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 22 (1983), S. 171-190 
    Details
    ISSN: 0570-0833
    Keywords: 1,4-Diazines ; Pyrazine ; Heterocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In chemical research attention is increasingly being focussed on composite “complex” systems with special properties and functions. As components of such systems 1,4-diazines are steadily gaining in popularity. Here, 1,4-diazines means pyrazine and its derivatives as well as compounds with partial pyrazine structure; examples are quinoxaline, phenazine, pteridine, flavin and their derivatives. All these compounds are characterized by a low lying unoccupied π-molecular orbital and by the ability to act as bridging ligand. Due to these two properties 1,4-diazines, and especially their parent compound pyrazine, possess a characteristic reactivity. 1,4-Diazines may be employed to study inter- and intramolecular electron transfer in organic, inorganic and biochemical reactions. In the redox system of 1,4-diazines the paramagnetic 7π-electron intermediate exhibits exceptional stability, whereas the 1,4-dihydro-1,4-diazines with 8π-electrons in a six-membered ring are not generally accessible due to their potential antiaromaticity and their large excess of π electrons. Its inherent bifunctionality and the low lying unoccupied molecular orbital permit pyrazine to form coordination polymers having unusual electrical and magnetic properties. Finally, the phenomena observed for pyrazines may be used in the interpretation of the reactivity of naturally occurring 1,4-diazines, such as flavins and bioluminescent natural products.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198301713
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  • 5
    Electronic Resource
    Electronic Resource
    Homolytic Cyclizations of N-ChloroalkenylaminesDedicated to Professor Jean-Marie Surzur on the occasion of his 50th birthday. (1983)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 22 (1983), S. 337-350 
    Details
    ISSN: 0570-0833
    Keywords: Cyclization ; Chloroamines ; Alkenylamines ; Synthetic methods ; Heterocycles ; Free radicals ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Many N-chloroalkylamines with double bond(s) dissociate homolytically to give chlorine atoms and aminyl radicals which undergo intramolecular cyclization reactions. Here, the nature of the aminyl radicals (neutral, protonated, or complexed to metal salts) appears to be important. The reactivity varies strongly from one species to another, and their selectivities can be different towards addition, substitution, abstraction, or dimerization reactions. A good synthetic tool appears to be the “complexed radical”, which is generated under mild conditions. A variety of β-functionalized, substituted, fused, or bridged azaheterocycles with alkaloid part structures thus become easily accessible in high yields, in a regio- and, possibly, stereoselective manner. Many examples are discussed illustrating the synthetic possibilities, limitations, and mechanistic features of this cyclization process.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198303373
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  • 6
    Electronic Resource
    Electronic Resource
    Complex Reducing Agents (CRA's) - Versatile, Novel Ways of Using Sodium Hydride in Organic Synthesis (1983)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 22 (1983), S. 599-613 
    Details
    ISSN: 0570-0833
    Keywords: Complex reducing agents ; Reduction ; Sodium hydride ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Why do we hardly use the simplest and, at the same time, inexpensive reducing agent sodium hydride in organic chemistry? To this question the answer is invariably: “It is too basic”. In this progress report we describe work we have performed aimed at controlling the basicity of NaH using sodium alcoholates and metal salts. The complex reducing agents (CRA's) developed (symbolized NaH-RONa-MXn) allow organic halides, alkenes, alkynes and ketones to be reduced selectively. Highly regioselective 1,4- and 1,2-reductions of α,β-unsaturated ketones are easily performed using appropriate metal salts. Modified CRA's have proved to be excellent hydrosilylating reagents for carbonyl groups, non-pyrophoric heterogeneous hydrogenation catalysts, coupling reagents for aryl and vinyl halides, and reagents for the carbonylation of organic halides under very mild conditions. The study of these reactions opened up the field to phase-transfer-catalyzed photostimulated carbonylations as well as to SRN1 reactions of metalates.-Thus, starting from the simple sodium hydride a large number of useful reagents have become accessible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198305991
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