Homologation of Alkenyl Carbonyls via a Cyclopropanation/Light-Mediated Selective CÀ C Cleavage Strategy

We report herein our studies on the direct photoactivation of carbonyl cyclopropanes to give biradical intermediates, leading to selective cleavage of the more substituted carbon-carbon bond. Depending on the substrate structure, extended alkenes were isolated or directly reacted in a photo-Nazarov process to give bicyclic products. Based on these results, a unified reductive ring-opening reaction was developed by using diphenyl disulfide as a hydrogen atom transfer (HAT) reagent. By performing a sequential cyclopropanation/ selective ring opening reaction, we achieved a CH 2 insertion into the α,β bond of both acyclic and cyclic unsaturated carbonyl compounds. Our protocol provides a further tool for the modification of the carbon framework of organic compounds, complementing the recent progress in "skeletal editing".