Palladium-catalyzed oxidative carbocyclization-borylation of enallenes to cyclobutenes

Abstract

A highly efficient palladium-catalyzed oxidative borylation of enallenes was developed for the selective formation of cyclobutene derivatives and fully-substituted alkenylboron compounds. Cyclobutenes are formed as the exclusive products in MeOH in the presence of H2O and Et3N, whereas the use of AcOH leads to alkenylboron compounds. Both reactions showed a broad substrate scope and good tolerance for various functional groups, including carboxylic acid ester, free hydroxy, imide, and alkyl groups. Furthermore, transformations of the borylated products were conducted to show their potential applications. Fair and square: An efficient palladium-catalyzed oxidative borylating carbocyclization of enallenes to cyclobutene derivatives was developed. Cyclobutenes are produced as the exclusive products in MeOH in the presence of H2O with a catalytic amount of Et3N, whereas the formation of alkenylboron compounds is favored in AcOH. Broad substrate scope and good tolerance for various functional groups could be achieved in both reactions.