A FEW NEW METHODS FOR ASYMMETRIC-SYNTHESIS

Aza-Claisen rearrangement of N-2(E)-butenyl-N-butylpropanamide was found to proceed smoothly at~135°C in the presence of LDA to furnish syn-N-butyl-2,3-dimethyl-4-pentenamide in~94% yield and >99% de. The reaction with the corresponding N-(1S)-1-phenethyl derivative yielded (2R,3S)-N-[(1S)-1-phenethyl] -2,3-dimethyl-4-pentenamide in 83% de. An efficient and generally-applicable two-step procedure for the hydrolysis of N-monosubstituted amides was also developed and the corresponding carboxylic acids were obtained in good yields without any epimerization at the α-position of the acyl group. The amines used for the chiral induction can be recovered in 71% yield. © 1990 De Gruyter