Synthesis of 6Benzo[]chromene Scaffolds from -Benzylated Phenols through a C-H Sulfenylation/Radical Cyclization Sequence.

-Aryl dibenzothiophenium salts, obtained through a highly regioselective C-H sulfenylation of -benzyl-protected phenols, are used as precursors of 6-benzo[]chromenes. The reaction starts with a photocatalytically triggered single-electron transfer to the sulfonium salt, which promotes the formation of an aryl radical via selective mesolitic cleavage of the S-Ar bond. Mechanistic studies reveal that this initial radical species cyclizes following a kinetically favored 5-exo-trig pathway. Subsequent ring expansion, favored by rearomatization, delivers the desired tricyclic systems.