Chemodivergent Chalcogenation of Aryl Alkynoates or N‑Arylpropynamides Using 9‑Mesityl-10-Methylacridinium Perchlorate Photocatalyst

Herein we report a cascaded chalcogenation of aryl alkynoates or N-arylpropynamides using 9-mesityl-10-methylacridinium perchlorate as a visible light photocatalyst to obtain selectively either 3-sulfenylated/selenylated coumarins or spiro­[4,5]­trienones. In a radical initiated process, the spiro-cyclization reaction was favored due to the presence of a -OMe or -F substituent at the para position of the aryl group, which helped to stabilize the allylic radical intermediate formed during the reaction. Otherwise, 6-endo-trig cyclization led to 3-sulfenylated/selenylated coumarins. Overall, the new C–S/C–Se, C–C, and CO bonds were formed in a single step. The Stern–Volmer quenching study, EPR experiments, light ON-OFF experiments, radical trapping experiments, etc., helped to understand the radical-based mechanism.