Regioselectivity in the reaction of tantalum-unsymmetrical acetylene complexes with carbonyl compounds. Stereoselective preparation of 1-alkenyl sulfides, .alpha.,.beta.-unsaturated esters, and amides
摘要:
Tantalum-alkyne complexes, derived by treatment of alkynes with low-valent tantalum (TaCl5 and zinc), react in situ with carbonyl compounds to give (E)-allylic alcohols stereoselectively. When unsymmetrical acetylenes are employed in the reaction, two regioisomeric allylic alcohols are produced. The regioselectivity of the reaction depends on the steric and electronic effects of the substituents on the acetylenes. For example, treatment of tantalum-alkyne complexes derived from methyl alkynyl sulfides with carbonyl compounds yields (E)-3-hydroxy-1-propenyl methyl sulfides in a regioselective manner. Tantalum-alkyne complexes derived from acetylenic esters react with carbonyl compounds regioselectively at the alpha-position of the esters to give Z-isomers of trisubstituted alpha,beta-unsaturated esters. In contrast, tantalum-alkyne complexes derived from acetylenic amides react with carbonyl compounds predominantly at the beta-position of the amides. The regioselectivity of the reaction between acetylenic amides and aldehydes, however, cannot be explained solely in terms of the steric and electronic effects of the substituents. Strong coordination of the amide group to the tantalum center could also be responsible for the observed selectivity, which is opposite to that observed with tantalum-acetylenic ester complexes.
Preparation of 1-alkynyl 2-(trimethylsilyl)ethyl sulfides as thiolate anion precursors for self-assembled monolayers
摘要:
Syntheses of 1-alkynyl 2-(trimethylsilyl)ethyl sulfides are reported. Deprotection of 2-(trimethylsilyl)ethyl groups using fluoride ions permits the formation of thiolate anions which are trapped by in situ alkylation with methyl iodide and can be used to produce self-assembled monolayers on gold. (C) 1998 Elsevier Science Ltd. All rights reserved.
Copper-Catalyzed Extended Pummerer Reactions of Ketene Dithioacetal Monoxides with Alkynyl Sulfides and Ynamides with an Accompanying Oxygen Rearrangement
and ynamides provided a wide variety of γ,γ‐disulfanyl‐β,γ‐unsaturated carbonyl compounds with an accompanying oxygen rearrangement. The products can be easily converted into 1,4‐dicarbonyl compounds and substituted heteroaromatics. DFT calculations and mechanistic experiments revealed a new interesting stepwise addition/oxygen rearrangement mechanism.
Selective Cyclotrimerization of Acetylenes<i>via</i>Tantalum-Alkyne Complexes
作者:Kazuhiko Takai、Masashi Yamada、Kiitiro Utimoto
DOI:10.1246/cl.1995.851
日期:1995.9
Tantalum-alkyne complexes prepared from internal acetylenes and low-valent tantalum (TaCl5 and Zn) in DME and benzene react with terminal diynes in the presence of THF and pyridine to give tetrasubstituted benzene derivatives in good to excellent yields.
produces tantalum-alkyne complexes (not isolated), which react in situ with phenyl isocyanate (or butyl isocyanate) to give (E)-α,β-unsaturated amides stereoselectively. The tantalum–alkyne complexes also react with acyl cyanides in the presence of BF3·OEt2 to give α-cyanohydrins. In both reactions, filtration of the reaction mixture containing the tantalum–alkyne complexes before addition of isocyanates
Reaction of Tantalum–Alkyne Complexes with Isocyanates Leading to (<i>E</i>)-α,β-Unsaturated Amides. Stereoselective Functionalization of Carbon-Carbon Triple Bonds
alkynes with low-valent tantalum derived from TaCl5 and zinc produces tantalum-alkyne complexes (not isolated), which react with phenylisocyanate (or butylisocyanate) to give (E)-α,β-unsaturated amidesstereoselectively.
Treatment of tantalum-alkyne complexes with dimethylhydrazones by the assistance of Me 3 Al in a mixed solvent of DME, benzene, and THF at 45°C for 16 h gives (E)-allylic hydrazines stereoselectively
在二甲醚、苯和四氢呋喃的混合溶剂中,在 Me 3 Al 的帮助下,在 45°C 下用二甲基腙处理钽-炔配合物 16 小时,立体选择性地得到 (E)-烯丙基肼