Solvolysis of endo- and exo-bicyclo[3.2.1]octan-3-yl toluene-p-sulphonates. Part 1. Product analysis

Abstract

Bicyclo[3.2.1]octan-3-yl tosylates (1a) and (2a) have been solvolysed in buffered acetic and formic acids, and buffered 98 and 50% aqueous ethanol. Major reactions in all solvents are elimination and unrearranged substitution with inversion of configuration. The amount of rearrangement is solvent dependent ranging from 1.7% for (2a) in 98% aqueous ethanol to 37.4% for (1a) in formic acid, and from (1a) and (2a) comprises the exo-bicyclo[3.2.1 ]octan2-yl and bicyclo[2.2.2]octan-2-yl compounds (3) and (5) in similar amounts with (usually)endo-bicyclo[3.2.1]octan-2-yi compounds (4) in much lower yield. In all cases, the yield of unrearranged substitution product of retained configuration is very low (0.2–0.8%) and no rearranged alkene was detected at all. We suggest that whereas (1a) reacts through a chair cyclohexane conformation, (2a) reacts largely through a boat cyclohexane conformation. From both (1a) and (2a), an unsymmetrical non-classical cation (8), formed via classical bicyclo[3.2.1]octan-2-yl cations, is invoked to account for the bulk of the two major rearrangement products (3) and (5), with only much smaller amounts of rearrangement occurring directly from the classical intermediates or via the symmetrical non-classical cation (9).