The Reaction of N-(Ethoxycarbonyl)phthalimide with Aniline

Abstract

The reaction of N-(ethoxycarbonyl)phthalimide (ECPI) with aniline was investigated. Two new reaction intermediates, N-ethoxycarbonyl-N'-phenylphthalamide (ring-opening adduct [1]) and 1-ethoxycarbonylamino-1-hydroxy-2-phenylisoindoline-3-one (isoindolone [2]), were isolated as stable compounds. These intermediates [1] and [2] were converted into N-phenylphthalimide [3] in a quantitative yield with the elimination of urethane at 150-480° C. The reaction of ECPI with aniline was markedly influenced by the temperature and the catalyst. In the neutral solution of tetrahydrofuran, the reaction gave [1] or [3] at room temperature or at a temperture above 60° C, respectively. In the presence of basic catalyst such as triethylamine and aqueous sodium carbonate, the reaction yielded the imide (3) selectively, whereas the iso- indolone (2) was obtained in the presence of such an acidic catalyst as aqueous acetic acid. From these results, it may be concluded that the reaction gives first the ring-opening adduct [1], which is subsequently isomerized to the isoindolone [2] and the latter compound [2] is finally converted into N-phenylphthalimide [3] with the elimination of urethane.