Visible Light-Induced and Singlet Oxygen-Mediated Photochemical Conversion of 4-Hydroxy-α-benzopyrones to 2-Hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxamides/carboxylates Using Rose Bengal as a Photosensitizer.

Development of a visible light-induced and singlet oxygen-mediated green protocol has been accomplished for the first time for the photochemical transformation of 4-hydroxy-α-benzopyrones to a new series of biorelevant 2-hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxamides and 2-hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxylates using rose bengal as a triplet photosensitizer at ambient temperature. Metal-free one-pot synthesis, broader substrate scope, good-to-excellent yields, use of cost-effective and eco-friendly starting materials and photosensitizer, and energy efficiency are the salient features of this newly developed method.