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.

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) in a total yield of 98%. The probable mechanism of their formation through tantalacyclopentanes as key intermediates is discussed.Figure optionsDownload as PowerPoint slideHighlights
► TaCl5-catalyzed alkene carbomagnesiation with EtMgX proceeds via two parallel routes.
► The labile tantalacyclopentanes are proposed as key intermediates in this reaction.
► Carbomagnesiation mediated by TaCl5 successfully occurs in tetrahydrofuran.
► 2- And unusual 3-(R-substituted)-n-butylmagnesiums are obtained in 98% total yield.