Multifaceted Substrate–Ligand Interactions Promote the Copper-Catalyzed Hydroboration of Benzylidenecyclobutanes and Related Compounds
Taeho Kang, Tuğçe G. Erbay, Kane L. Xu, Gary M. Gallego, Alexander Burtea, Sajiv K. Nair, Ryan L. Patman, Ru Zhou, Scott C. Sutton, Indrawan McAlpine, Peng Liu, Keary M. Engle
Abstract
A unified synthetic strategy to access tertiary four-membered carbo/heterocyclic boronic esters is reported. The use of a Cu(I) catalyst in combination with a modified 1,2-bis(diphenylphosphino)benzene (dppbz) ligand enables regioselective hydroboration of various trisubstituted benzylidenecyclobutanes and carbo/heterocyclic analogs. The reaction conditions are mild, and the method tolerates a wide range of medicinally relevant heteroarenes. The protocol can be conveniently conducted on a gram scale, and the tertiary boronic ester products undergo facile diversification into valuable targets. Reaction kinetics and computational studies indicate that the migratory insertion step is turnover-limiting and accelerated by electron-withdrawing groups on the dppbz ligand. Energy decomposition analysis calculations reveal that electron-deficient P-aryl groups on the dppbz ligand enhance the T-shaped π/π interactions with the substrate and stabilize the migratory insertion transition state.