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  • C-C coupling  (2)
  • Heterocycles  (2)
  • Titanium complexes  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Übergangsmetallaktivierte organische Verbindungen, XXXVII. über eine neue Aldehyd-und Ketonreaktion: Synthese und spektroskopische Untersuchung von α1-Phosphonioalkoxy-übergangsmetallkomplexenHerrn Professor Ulrich Schöllkopf zum 65. Geburtstag gewidmet. (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 453-457 
    Details
    ISSN: 0009-2940
    Keywords: Aldehydes ; Ketones ; Titanium complexes ; Niobium complexes ; Tantalum complexes ; Phosphonium chlorides ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transition Metal-Activated Organic Compounds, XXXVII[1].  -  A Novel Reaction of Aldehydes and Ketones: Synthesis and Spectroscopic Investigation of α1-Phosphonioalkoxy Transition Metal ComplexesHerrn Professor Ulrich Schöllkopf zum 65. Geburtstag gewidmet.By treatment of aldehydes and ketones with one mole equivalent of a Lewis acid (TiCl4, NbCl5, TaCl5) and one mole equivalent of PPh3, or in one case of Ph2PCH2CH2PPh2, the aldehyde derivates [R1CH(P+Ph2R2)-OMCln]Cl- (4-8; M=Ti, Nb, Ta; R2=Ph or CH2CH2PPh2) and the ketone derivatives [R1R2C(P+Ph3)-ONbCl4]Cl- (9-10) were prepared. Complexes 4-10 were isolated as air-and water-sensitive solids. According to the NMR spectra some of the obtained aldehyde derivatives 4-8 exist in solution as a mixture of isomers or oligomers, whereas the ketone derivatives 9 and 10 form in solution an equilibrium with the free ketone and the complex NbCl5 · PPh3. The chloride ion of 4-10 is perhaps coordinated to the metal.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260224
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  • 2
    Electronic Resource
    Electronic Resource
    Übergangsmetallaktivierte organische Verbindungen, XXXVIII. Chemoselektive nucleophile Methylierungen durch In-Situ-Blockierung von Aldehydgruppen unter α1-Phosphonioalkoxid-BildungHerrn Professor Ulrich Schöllkopf zum 65. Geburtstag gewidmet. (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 459-464 
    Details
    ISSN: 0009-2940
    Keywords: Chemoselectivity ; Titanium complexes ; Niobium complexes ; Tantalum complexes ; Methylation of aldehydes and ketones ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transition Metal-Activated Organic Compounds, XXXVIII[1].  -  Chemoselective Nucleophilic Methylation Reactions by In-Situ-Blocking of Aldehyde Groups by α1-Phosphonioalkoxide FormationHerrn Professor Ulrich Schöllkopf zum 65. Geburtstag gewidmet.For the selective methylation of a keto group in the presence of an aldehyde group the complex MeTiCl3·PPh3 and especially the reagent system [TiC]4·PPh3 + 0.5 Me2Zn] proved to be favourable. For instance, 6-oxoheptanal (8) was methylated by [TiCl4·PPh3 + 0.5 Me2Zn] at the keto group with 89% yield and 99:1 selectivity, whereas it was methylated by [TiCl4 + 0.5 Me2Zn] at the aldehyde group with 81% yield and 96:4 selectivity. A selective methylation of benzaldehyde in the presence of heptanal was achieved with MeNbCl4·PPh3 or [NbCl5·PPh3 + 0.75 Me2Zn] to give (1-chloroethyl)benzene (14; yield 92 or 53%; selectivity in each case 93:7) or with [TaCl5·PPh3 + 1.5 Me2Zn] to give mainly 1-phenylethanol (15) besides 16. A 96:4-selective benzylation (yield 74%) of a ketone in the presence of an aliphatic aldehyde was possible with [TiCl4·PPh3 + 1 PhCH2MgBr].  -  The high chemoselectivity is caused by irreversible blocking of aliphatic aldehyde groups by α1-phosphonioalkoxide formation[1], whilst the corresponding reaction of keto groups[1] and of benzaldehyde is reversible.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260225
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  • 3
    Electronic Resource
    Electronic Resource
    Progress in the Hetaryne FieldHetarynes, Part 15.-Part 14, see ref. [15].Dedicated to Professor Wilhelm Klemm on the occasion of his 75th birthday (1971)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 10 (1971), S. 20-33 
    Details
    ISSN: 0570-0833
    Keywords: Hetarynes ; Heterocycles ; Alkynes ; Arynes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: During recent years, instead of concentrating on the detection of the intermediacy of new hetarynes, as they did between 1958 and 1964, workers in this field have been more concerned with the critical sifting and checking of the earlier work. Special interest has been shown in the relation between structure and reactivity in the hetarynes. It has been shown that in addition to the elimination-addition mechanism (EA; hetaryne intermediate), other reaction paths (anomalous addition-elimination mechanism [AEa] and “Reinecke mechanism”) are possible for nucleophilic cine-substitutions on hetaryl halides. The use of deuterated hetaryl halides has proved very valuable for the elucidation of the mechanism of nucleophilic substitutions. Even where substitution mechanisms are superimposed on one another the occurrence of a hetaryne intermediate can be detected by a technique known as the “base competition method”. A five-membered hetaryne (4,5-didehydro-1-methylimidazole) has been detected for the first time by this method with a probability that borders on certainty. Selectivity determinations have shown that the replacement of a CH group in 1,2-didehydrobenzene and in 1,2-didehydronaphthalene by an N atom distinctly increases the reactivity to bases. According to EHT (Extended Hückel Theory) calculations, the as yet hypothetical 2,3-didehydropyridine is richer in energy than 3,4-didehydropyridine, this agrees more closely with the experimental findings than the opposite result obtained from simple MO calculations. Besides cine-substitution (1,2 shift), tele-substitution (1,3-shift) has also been observed on reaction of hetaryl halides (pyridine, quinoline, and pyrimidine systems) with bases. An EA mechanism (via m-didehydrohetarenes) and an AEa mechanism are considered as alternatives for the tele-substitution.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.197100201
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  • 4
    Electronic Resource
    Electronic Resource
    From the Principle of Areno-Analogy to Heterocyclopolyaromatic CompoundsHeterocyclopolyaromatic Compounds, Part 8. - Part 7: ref. [40a].Dedicated to Georg Wittig (1979)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 18 (1979), S. 1-19 
    Details
    ISSN: 0570-0833
    Keywords: Areno-analogy ; Heterocyclopolyaromatic compounds ; Heterocycles ; Heteroaromatic compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Organometallic linkage of heteroaromatic compounds provided a means of synthesizing complicated combinations of heteroaromatic compounds; not only nucleophilic aromatic substitution, but also “Ar—Cu/Ar—Hal linkage”, “organometallic oxidative linkage”, and “metal amide linkage” have been employed. The heterocyclopolyaromatic compounds are made of one, two, or three kinds of heteroaromatic species as ring members. These syntheses illustrate the construction of heterocycles from large, performed structural units. Competition experiments showed that the reactivity typical of the individual species is enhanced in open-chain combinations (ArNu)n and (ArE)n (ArNu, ArE: nucleo- and electrophilic heteroaromatic systems, respectively); the opposite situation is mostly encountered in the case of ArNu—AE combinations. - Cycloocta[1,2-b:4,3-b′5,6-b″:8,7-b‴]tetrathiophene, the only heterocyclopolyaromatic system yet to have been studied in detail, proved surprisingly inclined to undergo monosubstitution reactions.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.197900013
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  • 5
    Electronic Resource
    Electronic Resource
    Novel Reactions of Organomolybdenum and Organotungsten Compounds: Additive-Reductive Carbonyl Dimerization, Spontaneous Transformation of Methyl Ligands into μ-Methylene Ligands, and Selective CarbonylmethylenationOrganomolybdenum- and Organotungsten Reagents, Part 7. Part 6: [1]. (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 36 (1997), S. 1258-1275 
    Details
    ISSN: 0570-0833
    Keywords: C—C coupling ; carbonylmethylenation ; μ-methylene complexes ; molybdenum ; tungsten ; Carbonyl methylenation ; C-C coupling ; Bridging ligands ; Molybdenum ; Tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hitherto there was no reaction known that permits transformations of R1R2-CO → 0.5 R1R2R3C-CR1R2R3 in one step. This type of additive-reductive carbonyl dimerization is now possible using alkoxy(alkyl)tungsten(v) complexes with aromatic, heteroaromatic or α,β-unsaturated aldehydes and ketones. When a corresponding phenyl complex was employed in a test experiment, it was revealed that an aliphatic ketone could be used as the substrate in this reaction. A second interesting type of reaction is the transformation of CH3 ligands into μ-CH2 ligands, which occurs during the treatment of MeLi or Me3Al with molybdenum or tungsten chlorides (oxidation states VI and V, for Mo additionally IV) at low temperatures with liberation of CH4. Here, the question arises as to whether the intermediate involved has a terminal CH2 ligand (Schrock carbene complex) or a μ-CH3 ligand (CH3 bound by a two-electron three-center bond to two metal atoms). Of all the μ-CH2 complexes obtained, those which were synthesized by the action of MeLi on molybdenum chlorides can be recommended as reagents for carbonylmethylenation of aldehydes and ketones. They display high selectivity, very low basicity, a surprising resistance to protons, they are readily available, can be easily modified and, as regards their selective behavior, they have been investigated more thoroughly than other readily accessible carbonylmethylenation reagents of comparable selectivity. The results of NMR spectroscopic investigations on the structure of the μ-CH2 complexes, and associated reaction mechanisms are discussed. A survey of carbonylmethylenation reagents, which have been reported in the literature, permits comparisons to be made with carbonylmethylenating molybdenum and tungsten complexes.
    Additional Material: 9 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.199712581
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  • 6
    Electronic Resource
    Electronic Resource
    Oxidative Coupling via Organocopper CompoundsProtophanes and Polyarenes, Part 13. Part 12: [94].Dedicated to Professor Heinrich Hellmann on the occasion of his 60th birthday (1974)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 13 (1974), S. 291-305 
    Details
    ISSN: 0570-0833
    Keywords: C-C coupling ; Organocopper compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The type of reaction described here, which achieved preparative importance before the turn of the century in the form of the Glaser reaction, has found new applications in recent years: Syntheses of 1,3-dienes, 2,3,6,7-tetraaza-1,3,5,7-tetraenes, 2,3-diaza-1,3-dienes, hydrazine derivatives, bis(heteroallyl) compounds, hetarenes, polyhetarenes, cyclopolyarenes, protophanes, phanes, and heteraprotophanes. The reaction, which consists in the metalation of the starting substance followed by oxidative coupling of the metal derivative, merits special preparative interest when several successive coupling processes are possible (e. g. polyyne, polyarene, cyclopolyarene, and protophane syntheses). The main factors limiting its applicability are the high thermal stability of some organic copper compounds and the disproportionation of the ligands that frequently occurs as a competing reaction. Selective asymmetric linkages are not generally possible by this method.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.197402911
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