Two routes of tantalum-catalyzed alkene carbomagnesiation with ethyl Grignard reagents

Carbomagnesiation of 1-alkenes with EtMgX (X = Cl, Et) has been implemented in the presence of TaCl5 as a catalyst to give a mixture of 2-(R-substituted)-and 3-(R-substituted)-n-butylmagnesiums (5: 4 ratio) ina total yield of 98%. The probable mechanism of their formation through tantalacyclopentanes as key intermediates is discussed. (C) 2012 Elsevier B. V. All rights reserved.