PURPOSE: To provide the new compound useful as an intermediate for synthesizing various compounds, especially agricultural chemicals, medicines, etc.

CONSTITUTION: The compound of formula I (R1-a is H, alkyl; R2-a is a carboxyl- protecting group; but a case where the R1-a is H and R2-a is methyl or benzyl is excluded), e.g. N-(triphenylmethyl)-(S)-aziridine-2-carboxylic acid benzyl ester. The compound of formula I is obtained by subjecting a 2(S)- or 2(R)-, 3(R)-N- triphenylmethyl-3-haloalanine derivative of formula II (X is halogen; R1 is H, alkyl; R2 is a carboxyl-protecting group) to an intramolecular cyclization reaction in the presence of a weak base (e.g. KHSO3) in a nitrile solvent at room temperature to 150°C. The compound of formula I can be obtained from an inexpensive raw material in a good yield.