Carbopalladation of C-C σ-bonds enabled by strained boronate complexes.

Transition-metal-catalysed cross-coupling reactions, particularly those mediated by palladium, are some of the most broadly used chemical transformations. The fundamental reaction steps of such cross-couplings typically include oxidative addition, transmetallation, carbopalladation of a π-bond and/or reductive elimination. Herein, we describe an unprecedented fundamental reaction step: a C-C σ-bond carbopalladation. Specifically, an aryl palladium(II) complex interacts with a σ-bond of a strained bicyclo[1.1.0]butyl boronate complex to enable addition of the aryl palladium(II) species and an organoboronic ester substituent across a C-C σ-bond. The overall process couples readily available aryl triflates and organoboronic esters across a cyclobutane unit with total diastereocontrol. The pharmaceutically relevant 1,1,3-trisubstituted cyclobutane products are decorated with an array of modular building blocks, including a boronic ester that can be readily derivatized.