Radical Silyl‐ and Germylzincation of Propargylic Alcohols
Abstract
The 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(sp 2)-Zn bond remains available for subsequent in-situ electrophilic substitution leading overall to net alkyne trans difunctionalization.
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