Asymmetric Synthesis of Aziridines by Reduction of N-tert-Butanesulfinyl α-Chloro Imines

摘要

Reduction of (R_S)-N-tert-butanesulfinyl α-halo imines afforded chiral aziridines in good to excellent yields. Upon reduction of (R_S)-N-tert-butanesulfmyl α-halo imines with NaBH_4 in THF, in the presence of 10 equiv of MeOH, (R_S,S)-β-halo sulfinamides were formed in excellent yield (up to 98%) with very good stereoselectivity (> 98:2). Simple treatment of the latter (R_S,S)-β-halo-tert-butanesulfinarnides 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 NaBH_4 to LiBHEt_3. (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 α-halo imines with LiBHEt_3 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.