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 C1insertion 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.