Armstrong Alan, Ahmed Ghafoor, Dominguez-Fernandez Belen, Hayter Barry R, Wailes J Steven
School of Chemistry, University of Nottingham, Nottingham NG7 2RD, U.K.
J Org Chem. 2002 Nov 29;67(24):8610-7. doi: 10.1021/jo026322y.
Several alpha-substituted N-carbethoxytropinones have been evaluated as catalysts for asymmetric epoxidation of alkenes with Oxone, via a dioxirane intermediate. alpha-Fluoro-N-carbethoxytropinone (2) has been studied in detail and is an efficient catalyst which does not suffer from Baeyer-Villiger decomposition and can be used in relatively low loadings. This ketone was prepared in enantiomerically pure form using chiral base desymmetrization of N-carbethoxytropinone. Asymmetric epoxidation catalyzed by 2 affords epoxides with up to 83% ee. Among other derivatives tested, the alpha-acetoxy derivative 7 affords the highest enantioselectivities.
