Copper-Catalyzed Triboration of Terminal Alkynes Using B2pin2: Efficient Synthesis of 1,1,2-Triborylalkenes

We report herein the catalytic triboration of terminal alkynes with B(2)pin(2) (bis(pinacolato)diboron) using readily available Cu(OAc)(2) and (PBu3)-Bu-n. Various 1,1,2-triborylalkenes, a class of compounds that have been demonstrated to be potential matrix metalloproteinase (MMP-2) inhibitors, were obtained directly in moderate to good yields. The process features mild reaction conditions, a broad substrate scope, and good functional group tolerance. This copper-catalyzed reaction can be conducted on a gram scale to produce the corresponding 1,1,2-triborylalkenes in modest yields. The utility of these products was demonstrated by further transformations of the C-B bonds to prepare gem-dihaloborylalkenes (F, Cl, Br), monohaloborylalkenes (Cl, Br), and trans-diaryldiborylalkenes, which serve as important synthons and have previously been challenging to prepare.