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

Rh catalyzed gem-difluorovinylcyclopropane (DF-VCP) rearrangement (which can also be named 1,3-sigma migratory ring expansion) has been developed to synthesize 2-cyclopentenones with high efficiency and a wide substrate scope. In this reaction, water as the oxygen source was used to convert the CF2 group of the substrates to a carbonyl group in the final products. Utility of the DF-VCP rearrangement to the total synthesis of (±)-15-nor-pentalenene, an advanced model of branched triquinane natural products, has also been achieved, further demonstrating the practice of the present reaction to build triquinane skeleton from highly substituted DF-VCPs. Of the same importance, the mechanism of this rearrangement has been investigated by conducting experiments and DFT calculations, showing that gem-difluoro ene as a ketene surrogate works here (changing CF2 group to C═O group in the catalytic cycle) to realize otherwise difficult reductive elimination of forming a C(sp3)-C(sp3) bond. This strategy could be applied to design further reactions in the future.