Solvolysis of [3-13C]-4-homoadamantyl tosylate. Limited degeneracy of 4- homoadamantyl cation via multiple Wagner-Meerwein rearrangement and vicinal hydride shifts under solvolytic conditions

Article abstract of DOI:10.1021/jo00079a039

The solvolysis of 4-homoadamantyl tosylate in methanol, acetic acid, and 2,2,2-trifluoroethanol yielded 4-substituted homoadamantane and 4- homoadamantene as major products, together with exo-2-substituted homoadamantane and 2,4-dehydrohomoadamantane. The analysis of carbon-13 label distribution in the products from the [3-¹³C]-labeled reactant, which provided results complementary to those of Nordlander's deuterium label experiments, showed that the 4-homoadamantyl cation is a classical ion that is rapidly rearranging via the degenerate Wagner-Meerwein process (k(w)). This equilibrium was more nearly complete in less nucleophilic solvents. Another possible degenerate rearrangement, 5,4-hydride shift (k(h)), was shown to be much slower (k(w)/k(h) = 140-760); most of the 4-substituted product is formed with no more than a single hydride shift. Thus, the potential 11-fold degeneracy of the 4-homoadamantyl cation through the two types of rearrangements is partially restricted by competing solvent attack (k(p)). The analysis of the label distribution for the recovered reactant revealed involvement of appreciable ion pair return (k(-i)). The relative rates of the four possible processes concerning the fate of 4-homoadamantyl cation were determined in acetic acid at 40 °C to be k(p):k(-i):k(w):k(h) = 1:3.0:9.7:0.068.