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