Chemoselective Boronic Ester Synthesis by Controlled Speciation

Control of boronic acid solution speciation is presented as a new strategy for the chemoselective synthesis of boronic esters. Manipulation of the solution equilibria within a cross-coupling milieu enables the formal homologation of aryl and alkenyl boronic acid pinacol esters. The generation of a new, reactive boronic ester in the presence of an active palladium catalyst also facilitates streamlined iterative catalytic C-C bond formation and provides a method for the controlled oligomerization of sp(2)-hybridized boronic esters.