Stereoselective azide cycloaddition to chiral cyclopentanone enamines

Article abstract of DOI:10.1016/S0957-4166(97)00239-5

The enamine derived from cyclopentanone and (2R,5R)-2,5-bis(methoxymethyl )pyrrolidine added ethyl N-mesylazidoformimidate [N₃C(OEt)NMs] and ethyl azidoformate (N₃CO₂Et) with high asymmetric induction (>95%), while the corresponding cyclohexanone enamine gave ring contraction products. With the same azides the cyclopentanone enamine, prepared from (S)-2-(methoxymethyl)pyrrolidine gave N-substituted α-amino cyclopentanones in moderate enantiomeric excess.