Visible-Light-Induced Intermolecular Dearomative Cyclization of 2-Bromo-1,3-dicarbonyl Compounds and Alkynes: Synthesis of Spiro[4.5]deca-1,6,9-trien-8-ones.

A visible-light-induced photocatalytic intermolecular dearomative cyclization of 2-bromo-1,3-dicarbonyl compounds and alkynes afforded biologically important spirocarbocycle structures in moderate to good yields via a 5-exo-dig radical cyclization under mild reaction conditions. A 5.0 mmol scale dearomatization reaction proceeded smoothly with 95% yield even when the catalyst loading was reduced to 0.1 mol %, suggesting that this method was suitable for large-scale synthesis.