gem -DifluoroVinylcyclopropane (DF-VCP) Rearrangement to Cyclopentenones Catalyzed by Rh: Reaction Development, Mechanism, and Application to the Total Synthesis of (±)-15- nor -Pentalenene

A serendipitously discovered Rh-catalyzed gemdifluorovinylcyclopropane (DF-VCP) rearrangement (also named as 1,3-sigma migratory ring expansion) has been developed to synthesize synthetically important 2- cyclopentenones, usually accessed by well-known reactions such as Pauson-Khand, Nazarov reactions. This DF-VCP rearrangement has high efficiency, a wide substrate scope, and can be easily operated (tolerant to both air and water). Experimental and quantum chemical investigation of the mechanism of this rearrangement showed that, the gemdifluoro ene acts as a ketene surrogate (gdFEKS), realized by using water to convert CF2 group to a C=O group and achieve otherwise difficult reductive elimination reaction of forming C(sp3)-C(sp3) bond. The mechanistic insights and new gdFEKS are helpful for designing new reactions in the future.