O-H hydrogen bonding promotes H-atom transfer from α C-H bonds for C-alkylation of alcohols

The efficiency and selectivity of hydrogen atom transfer from organic molecules are often difficult to control in the presence of multiple potential hydrogen atom donors and acceptors. Here, we describe the mechanistic evaluation of a mode of catalytic activation that accomplishes the highly selective photoredox alpha-alkylation/lactonization of alcohols with methyl acrylate via a hydrogen atom transfer mechanism. Our studies indicate a particular role of tetra-n-butylammonium phosphate in enhancing the selectivity for alpha C-H bonds in alcohols in the presence of allylic, benzylic, alpha-C=O, and alpha-ether C-H bonds.