Asymmetric synthesis of spiro 2-pyrrolidin-5-ones and 2-piperidin-6-ones

Abstract

Bicyclic lactams 14–17 are isomerised on treatment with aluminium trichloride in 1,2-dichloroethane to give spiro lactams in high yield and >3: 1 diastereoselectivity; from the structures of 19a and 22b determined by X-ray crystallography, it follows that the indenes 19 and 21 are formed preferentially with retention of configuration at the spiro carbon atom and the naphthalenes 20 and 22 with inversion.