Stereoselective synthesis of trisubstituted .alpha.,.beta.-unsaturated esters and amides via reactions of tantalum-alkyne complexes derived from acetylenic esters and amides with carbonyl compounds
作者:Kazuhiko Takai、Makoto Tezuka、Kiitiro Utimoto
DOI:10.1021/jo00021a005
日期:1991.10
Treatment of acetylenic esters with low-valent tantalum (TaCl5 and Zn) in DME and benzene produces tantalum-alkyne complexes (not isolated), which react with carbonyl compounds regioselectively at the alpha-position of the esters to give Z isomers of trisubstituted alpha,beta-unsaturated esters in a stereoselective manner. In contrast, tantalum-alkyne complexes derived from acetylenic amides react with carbonyl compounds at the beta-position of the amides predominantly.