Electronic Control of Stereoselectivity in the Metal Hydride Reductions of 1,2,3,4-Tetrahydro-1,4-methanonaphthalen-9-ones

Abstract Stereoselectivity in the metal hydride reduction of a series of substituted 1,2,3,4-tetrahydro-1,4-methanonaphthalen-9-ones was investigated in relation to their homoconjugation character. The observed stereoselectivity sequence was found to be parallel with the homoconjugation sequence: the portion of anti-attack increases as the benzene ring becomes electron-rich. The results are rationalized in terms of the transition state model proposed by Cieplak or of the contribution of the nonclassical carbocation in the transition state.