Asymmetric synthesis of beta-amino acids by addition of chiral enolates toN-acyloxyiminium ions and application for synthesis of optically active 5-substituted 8-methylindolizidines

[GRAPHICS] N-Acyloxyiminium species generated from nitrones with acyl halides are high ly reactive and can undergo reaction with soft nucleophiles such as enolate s. Optically active beta-amino acid derivatives can be prepared using chira l enolates bearing chiral auxiliary. The usefulness of the present method i s demonstrated by the enantioselective synthesis of (SR,8R,8aS)-5-cyano-8-m ethylindolizidine ((-)-7), which is a common key intermediate for 5-substit uted 8-methylindolizidines.