The Chemistry of Short-Lived α-Fluorocarbocations

The present study of the chemistry of short-lived alpha-fluorocarbocations reveals that even inactive methyl carbons can serve as nucleophiles, attacking a cationic center. This, in turn, facilitates the synthesis of a cyclopropane ring in certain triterpene backbones. We report the synthesis of compounds similar to 2, containing a bridgehead cyclopropane, and compounds of type 3 with an 11 membered bicyclic ring consisting of two bridgehead double bonds (anti-Bredt) within a triterpene skeleton. The synthesis involves three unconventional chemical processes: (a) a methyl group serving as a nucleophile; (b) the unexpected and unprecedented synthesis of a strained system in the absence of an external neighboring trigger; and (c) the formation of an 11-membered bicyclic diene ring within a triterpenoid skeleton. An alpha-fluorocarbocation mechanism is proposed and supported by density functional theory calculations.

Automated summary

The study shows that inactive methyl carbons can act as nucleophiles, attacking cationic centers and aiding in the synthesis of cyclopropane rings in certain triterpene backbones. Unconventional chemical processes were used to synthesize compounds with bridgehead cyclopropane or an 11-membered bicyclic structure within a triterpene skeleton. The proposed alpha-fluorocarbocation mechanism was supported by density functional theory calculations.