When an ester is a benzyl ester or allyl ester, carboxylic acid can be obtained under the same conditions as those generally used for the deprotection of a protecting group for a carboxylic acid compound (which are conditions described in publications such as T. W. Green and P. G. M. Wuts, ???Protective groups in Organic Chemistry, Second Edition???, John Wiley & Sons (1991), pp. 248-251).