Enantiodivergent hydroboration reactions of a racemic allenylsilane with diisopinocampheylborane and Curtin–Hammett controlled double asymmetric crotylboration reactions of (S)-E-α-phenyldimethylsilyl(ddiisopinocampheyl)-crotylborane

Abstract

The enantiodivergent hydroboration reactions of racemic allenylsilane (±)-4 with (dIpc)2BH and subsequent crotylboration of achiral aldehydes with the product crotylborane (S)-E-5 at −78 °C provide (E)-δ-silyl-anti-homoallylic alcohols 6 in 71–89% yield and with 93–96% ee. Intriguingly, mismatched double asymmetric crotylboration reactions of enantioenriched chiral aldehydes 20 with (S)-E-5 proceed under Curtin–Hammett control to give anti-β-hydroxylcrotylsilanes 24 as the only products.