Diastereoconvergence in NHC/photo dual-catalysis: stereoselective boroacylation of internal electron-poor alkenes

Abstract

Achieving diastereoconvergence in synthetic chemistry, particularly in photocatalytic radical systems, remains a significant yet challenging goal. Herein, we report a diastereoconvergent radical boroacylation enabled by cooperative N-heterocyclic carbene (NHC) and photocatalysis. Notably, the reaction consistently delivers syn-diastereoselective products, regardless of the starting alkene geometry—E, Z, or an E/Z mixture—demonstrating its diastereoconvergent nature. In contrast, when the conformational dynamics are restricted, as in the case of a rigid cyclic Z-alkene, the reaction yields the anti-diastereoisomer, providing diastereoconvergence of mechanistic support for the key role of the rotational flexibility of the intermediate alkyl radical. This protocol enabled efficient synthesis of over 50 examples of β-boryl ketones in good to excellent yields, with complete regioselectivity and diastereoselectivity. The broad applicability of this method is further underscored by its successful adaptation to the late-stage functionalization of drug-derived NHC-boranes. Mechanistic studies, including control experiments, photophysical measurements, kinetic investigations, and density functional theory (DFT) calculations, revealed the organocatalytic radical reaction pathway and provided insights into the origins of diastereoselectivity and kinetic behavior.