Mechanistic Centrality of Boron-Containing Complexes in α-Hydroxy C–H Alkylation of Alcohols Promoted by Photoredox and Hydrogen Atom Transfer Catalysis

Selective α-hydroxy C–H alkylation of alcohols can be achieved using boronic acid, photoredox, and hydrogen atom transfer (HAT) catalysis. The key intermediate undergoing HAT is pro-posed to be a tetracoordinate boron-ate complex, formed from diol substrate, boronic acid and bound quinuclidine, which also serves as the HAT catalyst. Our studies reveal electron-poor boronic acids result in increased reaction efficiency. Calculated BDEs demonstrate this electronic trend is not due to modulating bond strengths in the boron-substrate complexes, although bond weakening is observed. Electron-poor boronic acids lead to a more dynamic equilibrium between different species, which we propose to be a contributing factor to overall increased alkylation rates.