Photochemistry of resveratrol. Beyond the reactivity of metal‐free porphyrins immobilized on lignin

The photochemistry of resveratrol with singlet oxygen (1O2) under blue-LED irradiation is explored in the presence of three metal-free porphyrins as photosensitizers. Irradiation at 450 nm yields products of C.C bond scission, 6-electron electrocyclic ring closure, and [4 + 2] cycloaddition, including benzaldehydes, 2,4,6-trihydroxyphenanthrene, and resveratrol cyclic endoperoxide. The selectivity of the process is controlled by the structure of the metal-free porphyrin and by the nominal capacity of the blue-LED photon. The scope of the reaction is extended to sustainable heterogeneous photosensitizers produced by immobilization of metal-free porphyrins on lignin, the most abundant polyphenol in nature characterized by beneficial photochemical properties.