Radical Silyl‐ and Germylzincation of Propargylic Alcohols

Abstract

AbstractThe silyl‐ and germylzincation of terminal or internal propargylic alcohols by reaction with (Me3Si)3SiH/Et2Zn, [(Me3Si)3Si]2Zn/Et2Zn or Ph3GeH/Et2Zn is examined. These reactions proceed through the addition of silicon‐ or germanium‐centered radicals across the carbon≡carbon triple bond followed by the trapping by diethylzinc of the produced vinyl radical through homolytic substitution at the zinc atom. The influence of the hydroxy unit on the regio‐ and stereoselectivity of these reactions is discussed and compared to its role played in radical hydrosilylation and hydrogermylation reactions. Protocols developed to achieve the β‐regioselective silylzincation of propargyl alcohol and the α‐regioselective germylzincation of internal propargylic alcohols are particularly important, as they occur with trans stereoselectivity. For both procedures the C(sp2)−Zn bond remains available for subsequent in‐situ electrophilic substitution leading overall to net alkyne trans difunctionalization.