Visible-Light-Induced Intermolecular Dearomative Cyclization of Furans: Synthesis of 1-Oxaspiro[4.4]nona-3,6-dien-2-one.

A fac-Ir(ppy)(3)-catalyzed intermolecular dearomative cyclization of 2-bromo-2-((5-bromofuran-2-yl)methyl)-malonate and alkynes affording substituted spirolactones in yields of 19-91% via a 5-exo-dig radical cyclization under visible light is presented. This method provides a new access to the synthesis of spirocycle skeletons applying water as an external oxygen source under mild reaction conditions.