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 sp2‐hybridized boronic esters. Under control: Controlling boron solution speciation during Suzuki–Miyaura cross‐coupling enables the chemoselective synthesis of functionalized boronic acid pinacol esters. A rapid Suzuki–Miyaura reaction followed by controlled pinacol recycle enables the formal homologation of sp2 boronic acid pinacol esters. The reaction can also be used for controlled oligomerization of sp2‐hybridized boronic esters. MIDA=N‐methyliminodiacetic acid, Pin=pinacol.