A Pd-catalyzed organometallic-free homologation of arylboronic acids enabled by chemoselective transmetalation

Abstract

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.

Ni-Catalyzed 1,2-Alkyl Borylation and Silylation of Allenes En Route to [1,3]-Bis-Organometallic Reagents

“…Herein, we report the realization of this goal, which culminates in a protocol that allows reliable access to [1,3]-bis-organometallics from a diverse set of allenes and ambiphilic reagents (Scheme 2), including the always elusive secondary α-haloboranes that are typically problematic when utilized as counterparts in catalytic functionalization of unsaturated compounds. 5,12 We began our investigations by studying the reaction of 1a with 2a and B 2 Pin 2 (Table 1). The choice of 2a was not arbitrary, given that (a) α-haloboranes are easily accessible from the Matteson homologation 13 and that (b) 3a would possess both sp 2 and sp 3 hybridization, thus giving ample room for chemoselective derivatization via cross-coupling reactions.…”