Patent ID: 7799929

Claim:
A process for preparing a compound represented by the formula (III): wherein R 1 and R 2 may be the same or different from each other, and each represents a hydrogen atom, a benzyl group which may have a substituent(s) on the benzene ring, a benzhydryl group which may have a substituent(s) on the benzene ring, or a trityl group which may have a substituent(s) on the benzene ring, which comprises subjecting a compound represented by the formula (II-a): wherein R 1 and R 2 have the same meanings as defined above, and R 3 represents a cyano group, carboxyl group, an alkoxycarbonyl group, an alkylthiocarbonyl group, or a carbamoyl group which may have a substituent, or a salt thereof to ring conversion to prepare a compound represented by the formula (I): wherein R 1 , R 2 and R 3 have the same meanings as defined above, or a salt thereof, subjecting the compound to hydrolysis, depending on the necessity to prepare a compound represented by the formula (I-a): wherein R 1 and R 2 have the same meanings as defined above, or a salt thereof, and then, subjecting the resulting Compound (I-a) to cyclization and epimerization.