Asymmetric synthesis of aziridines by reduction of N-tert-butanesulfinyl α-chloro imines

Reduction of (R-S)-N-tert-butanesulfinyl alpha-halo imines afforded chiral aziridines in good to excellent yields. Upon reduction of (R-S)-N-tert-butanesulfinyl alpha-halo imines with NaBH4 in THF, in the presence of 10 equiv of MeOH, (R-S,S)-beta-halo sulfinamides were formed in excellent yield (up to 98%) with very good stereoselectivity (> 98:2). Simple treatment of the latter (R-S,S)-beta-halo-tert-butanesulfinamides with KOH afforded the corresponding (R-S,S)-N-(tert-butylsulfinyl)aziridines in quantitative yields. On the contrary, its epimer, (R-S,R)-N-(tert-butylsulfinyl)aziridine was synthesized by switchover of the reducing agent from NaBH4 to LiBHEt3. (R-S,R)-N-(tert-Butylsulfinyl)aziridines were synthesized in good yields (up to 85%) and diastereoselectivity (up to 92:8) by reduction of (R-S)-N-tert-butanesulfinyl alpha-halo imines with LiBHEt3 in dry THF and subsequent treatment with KOH. All chiral aziridines were obtained as a single diastereomer after recrystallization (overall yield up to 91%) or after flash chromatography.