Diastereo- and Enantioselective Reactions of Bis(pinacolato)diboron, 1,3-Enynes, and Aldehydes Catalyzed by an Easily Accessible Bisphosphine–Cu Complex

Catalytic enantioselective multicomponent processes involving bis(pinacolato)diboron [B2(pin)2], 1,3-enynes, and aldehydes are disclosed; the resulting compounds contain a primary C-B(pin) bond, as well as alkyne- and hydroxyl-substituted tertiary carbon stereogenic centers. A critical feature is the initial enantioselective Cu-B(pin) addition to an alkyne-substituted terminal alkene. This and other key mechanistic issues have been investigated by DFT calculations. Reactions are promoted by the Cu complex of a commercially available enantiomerically pure bis-phosphine and are complete in 8 h at ambient temperature; products are generated in 66-94% yield (after oxidation or catalytic cross-coupling), 90:10 to >98:2 diastereomeric ratio, and 85:15-99:1 enantiomeric ratio. Aryl-, heteroaryl-, alkenyl-, and alkyl-substituted aldehydes and enynes can be used. Utility is illustrated through catalytic alkylation and arylation of the organoboron products as well as applications to synthesis of fragments of tylonolide and mycinolide IV.