Photocyclization of 2-(alkylthio)ethyl benzoylacetates via remote proton transfer following charge-transfer interaction between excited ketone carbonyl and thioether chromophore

Abstract

Upon irradiation, 2-(alkylthio)ethyl benzoylacetates 1a–d undergo photocyclization to give eight-membered thia lactones 2. No photoreactivity is observed for 2-(benzylsulfonyl)ethyl benzoylacetate 1e the sulfur atom of which lacks lone pairs able to serve as donor electrons. The photocyclization takes place via 1,9-proton transfer following intramolecular charge-transfer interaction between the sulfur atom and the excited carbonyl group.