PerspectiveOrganic Chemistry

Enchained by visible light–mediated photoredox catalysis

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Science  18 Sep 2015:
Vol. 349, Issue 6254, pp. 1285-1286
DOI: 10.1126/science.aad0193

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Free radicals are exploited in biology, often through highly controlled enzymatic reactions, to drive many reactions that would be difficult via nonradical routes that transfer two electrons (1). In synthetic chemistry, visible-light photoredox catalysis has emerged as an economical and environmentally benign route for promoting free radical transformations in the lab (24). Although the initial light-sensitization steps are well established (5), insufficient attention has been dedicated to essential mechanistic features of the closed catalytic cycle (6). Several reports have hypothesized that these photocatalyzed reactions are terminated through a closed catalytic cycle, which delivers the final product and regenerates the ground state of the photosensitizer (PS). However, Cismesia and Yoon (6) highlight that some of the mechanistic proposals may be incomplete and may involve radical chains.