Regioselectivity on electroreductive transannular reaction of 7-methylenebicyclo[3.3.1]nonan-3-one

A competitive transannular reaction occurred to give 7-methyltricyclo[3.3.1 .0(3,7)]nonan-3-ol (5) and 1-adamantanol (6) in the non-mediated electrored uction of 7-methylenebicyclo [3.3.1]nonan-3-one (1) in N,N-dimethylformamid e. The apparent temperature dependence of the regioselectivity of the react ion may be attributed to the competitive operation of both kinetic and ther modynamic controls in the cyclization of the ketyl radical anion. The diffe rences in the parameter of activation between the 5-exo- and 6-endocyclizat ions of 1(.-), Delta DeltaH double dagger ((5-exo-6-endo)) and Delta DeltaS double dagger ((5-exo-6-endo)), were evaluated to be -3.1 kcal mol(-1) and -11 cal mol(-1) K-1, respectively. Semiempirical PM3 (RHF and UHF) calcula tions were also carried out to elucidate the reaction mechanism.