Unusual Regioselectivity of Pd(0)-Catalyzed Coupling Reaction of Electron-Deficient Alkenyl Halides with Allenic/Propargylic Zinc Reagents. Highly Selective Synthesis of 6-Phenylhex-5-yn-2(or 3)-enoates/Enitrile and 4-Phenyl-6-substituted-hexa-2,4,5-trienoates
作者:Shengming Ma、Aibin Zhang、Yihua Yu、Wei Xia
DOI:10.1021/jo991243g
日期:2000.4.1
The Pd(0)-catalyzed coupling reaction of electron-deficient alkenyl halides with the organozinc formed by the subsequent treatment of 1-phenylalk-1-yne with n-BuLi and ZnBr2 with or without a catalytic amount of HgCl2 was studied. Both the allene-formation- and the alkyne-formation-type coupling reactions were observed with high regio- and stereoselectivity: the reaction of 1-phenylprop-1-yne afforded 6-phenylhex-5-yn-2(or 3)-enoates and -enitriles, while the reaction of 1-phenylhex-1-yne formed 4-phenyl-6-substituted-hexa-2,4,5-trienoates. A plausible explanation for the regioselectivity was discussed. The double bonds in 6-phenylhex-5-yn-2-enoates were prone to migrate to the position conjugated with the carbon-carbon triple bonds to form 6-phenylhex-5-yn-3-enoates at higher temperature. The migration did not occur in absence of an excess amount of allenic/propargylic zinc reagent or at low temperature.