Photoredox-Mediated Deoxygenative Radical Additions of Aromatic Acids to Vinyl Boronic Esters and gem-Diborylalkenes

A new method to access beta-keto-gem-diborylalkanes, by direct deoxygenative radical addition of aromatic carboxylic acids to gem-dibortlalkenes, is described. The reaction proceeds under mild photoredox catalysis and involves the photochemical C-O bond activation of aromatic carboxylic acids in the presence of PPh3. It generates an acyl radical, which further undergoes an additional reaction with gem-diborylalkenes to form an alpha-gem-diboryl alkyl radical intermediate, which then reduces to the corresponding anion, which after protonation, affords the beta-keto-gem-diborylalkane product. Moreover, the same scenario has been extended to the vinyl boronic esters, for example, gem-(Ar, Bpin)-alkenes, and gem-(Alkyl, Bpin)-alkenes. Importantly, this protocol provides a general platform for the late-stage functionalization of bio-active and drug molecules containing a carboxylic acid group.