Cu-Catalyzed Z -Selective Carboboration of Acetylene with Hindered Michael Acceptors Enabled by a Buffering Borinate Additive

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.