Thermolytic Rearrangements of 1,1-Cyclopropanedimethanol Disulfonates: Cyclopropylcarbinyl Cations Revisited.

1,1-Cyclopropanedimethanol dimethanesulfonate (1a) and the corresponding ditosylate 1b underwent thermal rearrangement at 110-140 o C after melting. Short reaction time resulted in the formation of mixtures containing 1-(sulfonyloxy)cyclobutanemethanol sulfonates 5a,b (major), starting material, and 2-methylene-1,4-butanediol disulfonates 6a,b. Longerreaction times afforded complex conversion to disulfonates 6a,b, isolated in 49 and 62% yield, respectively. These reactions are postulated to proceed via initial carbocation formation, presumably interconverting bicylobutonium and cyclopropylcarbinyl cations, which exist as ion pairs in the melt