Preparation of phthalamic acid derivatives and ring closure to phthalimidobarbituric acids

Article abstract of DOI:10.1002/jhet.5570440606

(Chemical Equation Presented) Phthalamic acid derivatives with a barbiturate moiety were prepared from 5-amino-5-ethylbarbituric acids. To circumvent an undesired acetylation in glacial acetic acid during the preparation of phthalimidobarbituric acids, two routes were proven exemplarily. On the one hand, a phthalamic acid (6a) was isolated and subsequently cyclized with acetic anhydride to the corresponding phthalimide 2a. On the other hand, a phthalamic acid tert-butyl ester (5b) was successively treated with trifluoroacetic acid and trifluoroacetic anhydride to achieve heterocyclization to the phthalimide 2b. These routes might be useful for the preparation of other phthalimides derived from sterically hindered primary amines.