Inverted Diastereoselectivity in Asymmetric Aziridine Synthesis via Aza-Darzens Reaction of (2S)-N-Bromoacyl Camphorsultam

The aza-Darzens reaction of the chiral enolate derived from (2S)-bromoacetyl camphor sultam (1) with certain C-3-substituted N-diphenylphosphinyl imines gives mixtures of trans- and cis-aziridines. In some cases, only trans isomers are observed. A steric repulsion between the enolate halogen atom and this C-3-substituent is invoked to rationalize these observations.