Geminal dimetalation of alkylidene-type carbenoids with silylboranes and diborons

A novel and efficient method for gem-dimetalation of carbenoids has been demonstrated. Treatment of alkylidene-type lithium carbenoids with such an interelement compound as silylborane or diboron to generate the corresponding borate complex, followed by warming to room temperature, induced migration of the silyl or boryl group from a negatively charged boron atom to the carbenoid carbon to afford 1-boryl-1-silyl-1-alkenes or 1,1-diboryl-1-alkenes in good yields. Carbon–carbon bond forming transformations of the gem-dimetalated compounds mediated by boron or silicon is also described.