Synthesis of 2-Fluorobenzofuran by Photocatalytic Defluorinative Coupling and 5-endo-trig Cyclization

An alkyl radical-triggered dual C–F bond cleavage of α-CF3-ortho-hydroxystyrenes for the synthesis of 2-fluorobenzofurans was developed. The visible-light-induced defluorinative cross-coupling reactions of α-CF3-ortho-hydroxystyrenes with a variety of carboxylic acids produced gem-difluoroalkenes, which underwent SNV-type 5-endo-trig cyclization to give 2-fluorobenzofurans. Mechanistic studies indicated that the electron transfer between phenoxyl radicals and carboxylates was the major pathway for the generation of alkyl radicals.