Structure of the reaction product of 4-hydroxy-2,3- dioxo-4-phenylbutanoic acid 1,4-lactone with o-phenylenediamine

Abstract Examination of the structure of the yellow product ( 5a ), obtained by treating 4-hydroxy-2,3-dioxo-4-phenylbutanoic acid 1,4-lactone (4-phenyl-2,3-dioxobutyro-1,4-lactone) with two moles of o -phenylenediamine, by high-resolution 1 H-, 13 C-, and 15 N-n.m.r. spectroscopy, as well as by electron-impact mass spectrometry, confirmed without ambiguity the structure of the product as the quinoxaline amide 5a . When 4-hydroxy-2,3-dioxo-4-phenylbutanoic acid 1,4-lactone is treated with o -phenylenediamine, the Schiff base is first formed, which is then converted into a quinoxaline lactone ( 6a ). The excess of o -phenylenediamine then converted the quinoxaline lactone ( 6a ) into the yellow product ( 5a ).