Unimolecular rearrangements and fragmentations in the gas phase: [1,3] sigmatropic isomerizations and [2+2] cycloreversions

Trimethylsilyl ethers of 3-buten-2-ol, 1-vinylcyclopropanol, 1-vinylcyclobutanol, and cyclobutanol were treated with fluoride over a wide temperature range (-40 to 300°C) in a variable-temperature flowing afterglow-triple quadrupole device. The structures of the resulting alkoxides and enolates were probed by ion-molecule reactions and their collision-induced dissociation (CID) spectra. Activation energies were obtained for several anion-accelerated [1,3] sigmatropic rearrangements and [2+2] cycloreversions. The mechanisms for these isomerizations and fragmentations (stepwise versus concerted) and their synthetic potential are discussed.