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

Article abstract of DOI:10.1021/jo00063a039

1,1-Cyclopropanedimethanol dimethanesulfonate (1a) and the corresponding ditosylate 1b underwent thermal rearrangement at 110-140 deg 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.Longer reaction times afforded complete conversion to disulfonates 6a,b, isolated in 49 and 62 percent yield, respectively.These reactions are postulated to proceed via initial carbocation formation, presumably interconverting bicyclobutonium and cyclopropylcarbinyl cations, which exist as ion pairs in the melt.Crossover experiments with dimesylate 1a and ditosylate 1b offer support for the presence of ion pairs in the melt: internal return competed with external trapping of the intermediate cations.Reaction of 1a and 2-methylene-1,4-butanediol ditosylate (6b) gave a mixture in which 2-methylene-1,4-butanediol 1-mesylate 4-tosylate (8) predominated over the isomeric 4-mesylate 1-tosylate 7 by a 5:1 ratio.Crossover experiments with 6a and 6b indicated that partial allylic substitution was occurring for the open-chain products under the thermolysis conditions.Reaction of 1a with excess tetrabutylammonium tosylate at 114-15 deg C afforded mixed 1-(sulfonyloxy)cyclobutanemethanol sulfonates and 2-methylene-1,4-butanediol disulfonates formed competitively by internal return and tosylate interception.Acetolysis of 1a at 42-43 deg C afforded predominately products of internal return early on the reaction profile.Longer reaction times afforded predominately monoacetates while reactions run at 108-10 deg C afforded substantial amounts of diacetates.Acetolysis of 1-acetoxycyclobutanemethanol mesylate (12a) resulted in the substitution of the mesyloxy group with substantial rearrangement.