Silane-Controlled Diastereoselectivity in the Tris(pentafluorophenyl)borane-Catalyzed Reduction of α-Diketones to Silyl-Protected 1,2-Diols

B(C6F5)3-catalyzed bis(hydrosilylation) of α-diketones can give high diastereomeric excess of either meso/anti (small silanes and disilane reagents) or dl/syn (bulky silanes) silyl-protected 1,2-diols. This easily tuned diastereoselectivity is rationalized based on the classic Felkin−Anh model applied to a mechanism relying on Si−H abstraction by the electrophilic borane reagent.