Stereoselective Syntheses of ( E)-γ',δ-Bisboryl-Substituted syn-Homoallylic Alcohols via Chemoselective Aldehyde Allylboration.

The development of a novel ( Z)-α,δ-bisboryl-substituted crotylboron reagent is reported. Ni-catalyzed 1,4-diboration of dienylboronate provided the targeted crotylboronate in good yield with high regio- and stereoselectivity. Chemo- and stereoselective addition of this crotylboron reagent to aldehydes followed by protection of the resulting secondary hydroxyl group gave TES-protected homoallylic alcohols bearing an alkyl and a vinyl boronate groups with high stereoselectivities.