ino compound with a phenylacetic acid ester derivative having the formula ##STR13## wherein R1 and R2 have the same meanings as defined above, and Y represents a halogen atom such as bromine or iodine, or a residue of a sulfonic acid such as methanesulfonyloxy, benzenesulfonyloxy or p-toluenesulfonyloxy group, followed by hydrolyzing the thus formed hydroxyimino-substituted phenylacetic acid ester