Enantiodivergent hydroboration reactions of a racemic allenylsilane with diisopinocampheylborane and Curtin-Hammett controlled double asymmetric crotylboration reactions of ()--αphenyldimethylsilyl( diisopinocampheyl)-crotylborane.

The enantiodivergent hydroboration reactions of racemic allenylsilane (±)- with ( Ipc)BH and subsequent crotylboration of achiral aldehydes with the product crotylborane ()-- at -78 °C provide ()--silyl--homoallylic alcohols in 71-89% yield and with 93-96% ee. Intriguingly, mismatched double asymmetric crotylboration reactions of enantioenriched chiral aldehydes with ()-- proceed under Curtin-Hammett control to give -β-hydroxylcrotylsilanes as the only products.