Copper-Photocatalyzed 1,2-Boron Migrative Alkylation of β-Boryl NHPI Esters with Cyclopropanols.

Abstract

Organoboron compounds are highly useful compounds in chemical synthesis, and boron-migration chemistry has recently attracted substantial interest. Herein, we report a radical 1,2-boron migrative alkylation achieved by combining photocatalysis and copper catalysis. The β-boryl NHPI esters undergo a 1,2-boron shift to a translocated C-radical species, which is subsequently intercepted by an alkyl-copper intermediate formed through copper-catalyzed ring-opening of cyclopropanols. In this process, the 4,4',4''-tritert-butyl-2,2':6',2''-terpyridine, used as the ligand, plays a crucial role. Using this protocol, a diverse array of β,β-dialkyl boronates can be rapidly accessed. Moreover, this type of C(sp3)-C(sp3) cross-coupling strategy is applicable to the late-stage functionalization of natural product frameworks. Mechanistic studies involving radical-trapping, light-on/off, CV, UV-vis, and EPR experiments support the radical-type pathway and key intermediates, rationalizing the proposed catalytic cycle.