A copper-catalyzed carboboration of acetylene with Knoevenagel-type Michael acceptors has been achieved by using a bidentate phosphine ligand, affording Z-alkenyl boronates in good to excellent yields. This new catalytic system overcomes the limitations of our earlier NHC-Cu catalytic system. The addition of EtO-9-BBN as a buffering additive effectively suppresses undesired decomposition pathways via reversible interaction with alkoxides to form boronate complexes. The formation of the key boronate intermediate was confirmed by 11B NMR spectroscopy. This strategy offers an efficient route to Z-alkenyl boronates bearing two electron-withdrawing groups, complementing our previous catalytic system.
Wang et al. (Thu,) studied this question.