Enantioconvergent Hydroboration of a Racemic Allene: Enantioselective Synthesis of (E)-δ-Stannyl-anti-homoallylic Alcohols via Aldehyde Crotylboration

The enantioconvergent hydroboration of racemic allenylstannane (+/-)-1 with ((d)Ipc)(2)BH converts both enantiomers of (+/-)-1 into the enantioenriched crotylborane (S)-E-3. Subsequent crotylboration of aldehydes with (S)-E-3 provides (E)-stannyl-homoallylic alcohols 5 in good yields and with excellent enantioselectivity.