The problem to be solved is to provide a method for producing a compound having excellent activity as an ± 2 ´ ligand. The solution thereto is a method for producing a compound represented by the general formula (I) or a salt thereof by optical resolution: [in the formula, R 1 : a hydrogen atom or a C1-C6 alkyl group, and R 2 : a hydrogen atom or a protective group for the carboxy group]
