THERMOLYTIC REARRANGEMENTS OF 1,1-CYCLOPROPANEDIMETHANOL DISULFONATES- CYCLOPROPYLCARBINYL CATIONS REVISITED

1,1-Cyclopropanedimethanol dimethanesulfonate (1a) and the correspondi ng ditosylate lb underwent thermal rearrangement at 110-140-degrees-C after melting. Short reaction time resulted in the formation of mixtur es containing 1-(sulfonyloxy)cyclobutanemethanol sulfonates 5a,b (majo r), 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 % yield, respectively. These reactions are postulated to proceed via initial carbocation formation, presumably i nterconverting bicylobutonium and cyclopropylcarbinyl cations, which e xist as ion pairs in the melt. Crossover experiments with dimesylate l a and ditosylate lb offer support for the presence of ion pairs in the melt: internal return competed with external trapping of the intermed iate cations. Reaction of la 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 part ial allylic substitution was occurring for the open-chain products und er the thermolysis conditions. Reaction of la with excess tetrabutylam monium tosylate at 114-15-degrees-C afforded mixed 1-(sulfonyloxy)cycl obutanemethanol sulfonates and 2-methylene-1,4-butanediol disulfonates formed competitively by internal return and tosylate interception. Ac etolysis of la at 42-43-degrees-C afforded predominately products of i nternal return early on the reaction profile. Longer reaction times af forded predominately monoacetates while reactions run at 108-10-degree s-C afforded substantial amounts of diacetates. Acetolysis of 1-acetox ycyclobutanemethanol mesylate (12a) resulted in the substitution of th e mesyloxy group with substantial rearrangement.