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.