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.