Strain Release of Donor-Acceptor Cyclopropyl Boronate Complexes.

The reactivity of boronate complexes which resemble donor-acceptor cyclopropanes is described. The enantioenriched cyclopropyl boronate complexes were shown to undergo concerted 1,2-metalate rearrangement/ring opening upon activation with a Lewis acid. This method provides atom-efficient access to optically active γ-carbonyl boronic esters in moderate to excellent yields with complete enantiospecificity. Furthermore, a three-component variant of the reaction was established through in situ alkylation, and the synthetic utility of the products as chiral building blocks was demonstrated.