A 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 alpha-boryl effect. Simultaneous chemoselective transmetalation allows use of these 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 exper-iments that demonstrate the reactivity enhancement provided by the -boryl effect are provided, along with a description of the limitations of the formal homologation process.