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

An alkyl radical-triggered dual C-F bond cleavage of α-CF 3 - ortho -hydroxystyrenes for the synthesis of 2-fluorobenzofurans was developed. The visible-light-induced defluorinative cross-coupling reactions of α-CF 3 - ortho -hydroxystyrenes with a variety of carboxylic acids produced gem -difluoroalkenes, which underwent S N V-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.