An Olefinic 1, 2‐Boryl‐Migration Enabled by Radical Addition: Construction of gem‐Bis(boryl)alkanes. Issue 28 (27th May 2019) - Zhao, Binlin
Abstract: A series of in situ formed alkenyl diboronate complexes from alkenyl Grignard reagents (commercially available or prepared from alkenyl bromides and Mg) with B2 Pin2 (bis(pinacolato)diboron) react with diverse alkyl halides by a Ru photocatalyst to give various gem‐bis(boryl)alkanes. Alkyl radicals add efficiently to the alkenyl diboronate complexes, and the adduct radical anions undergo radical‐polar crossover, specifically, a 1, 2‐boryl‐anion shift from boron to the α‐carbon sp 2 center. This transformation shows good functional‐group compatibility and can serve as a powerful synthetic tool for late‐stage functionalization in complex compounds. Measurements of the quantum yield reveal that a radical‐chain mechanism is operative in which the alkenyl diboronates acts as reductive quencher for the excited state of the photocatalyst. Abstract : Boron to be mild : A mild catalytic system was developed for the preparation of gem ‐bis(boryl)alkanes via an olefinic 1, 2‐boryl‐migration. This method has good functional‐group compatibility and can serve as a powerful synthetic tool for late‐stage functionalization in complex compounds.