Regio- and stereoselective copper-catalyzed α,β-protoboration of allenoates: access to Z -β,γ-unsaturated β-boryl esters.

A highly efficient regio- and stereoselective method for allenoate borylation has been developed. Using CuCl and bis(pinacolato)diboron in methanol, a variety of allenoates underwent β-boration and α-protonation to afford the corresponding Z -β,γ-unsaturated β-boryl esters under mild conditions with up to 81% yields.