Aa. Bahajaj et al., ASYMMETRIC-SYNTHESIS OF SPIRO 2-PYRROLIDIN-5-ONES AND 2-PIPERIDIN-6-ONES, Journal of the Chemical Society, Chemical Communications, (21), 1994, pp. 2511-2512
Bicyclic lactams 14-17 are isomerised on treatment with alu minium tri
chloride in 1,2-dichloroethane to give spiro lactams in high yield and
>3:1 diastereoselectivity; from the structures of 19a and 22b determi
ned by X-ray crystallography, it follows that the indenes 19 and 21 ar
e formed preferentially with retention of configuration at the spiro c
arbon atom and the naphthalenes 20 and 22 with inversion.