Pd-Catalyzed Organometallic-Free Homologation of Arylboronic Acids Enabled by Chemoselective Transmetalation

A Pd-catalyzed homologation of arylboronic acids is reported. Halomethylboronic acid pinacol esters (Bpin) undergo a remarkably facile, yet rare, oxidative addition enabled by an α-boryl effect. Simultaneous chemoselective transmetalation allows use of these metalloid reagents for formal C₁ insertion to deliver benzyl Bpin products without the requirement for stoichiometric organometallic reagents. The utility of the process is demonstrated by stepwise C(sp³)-C(sp²) cross-coupling of the boronic ester products into diarylmethane pharmacophores and electrophile/nucleophile chemoselective cross-coupling. Control experiments that demonstrate the reactivity enhancement provided by the α-boryl effect are provided, along with a description of the limitations of the formal homologation process.