Copper-Catalyzed Tandem Hydrocupration and Diastereo- and Enantioselective Borylalkyl Addition to Aldehydes.

We report the copper-catalyzed stereoselective addition of in situ generated chiral boron-α-alkyl intermediates to various aldehydes including α,β-unsaturated aldehydes under mild conditions. This tandem and multicomponent method facilitated the synthesis of enantiomerically enriched 1,2-hydroxyboronates bearing contiguous stereocenters in good yield with high diastereo- and enantioselectivity up to a ratio greater than 98:2. In particular, α,β-unsaturated aldehydes were successfully used as electrophiles in Cu-H catalysis through 1,2-addition without significant reduction. The resulting 1,2-hydroxyboronates were used in various transformations.