Synthesis and characterization of isomeric cis- and trans-pyrrone model compounds

Isomeric cis- and trans-imidazopyrrolones, obtained from the reaction of pyromellitic di-anhydride and o-phenylenediamine, were prepared as models for pyrrone polymers. The characterization of these model compounds, which represent the repeat unit of the completely cyclized polymer, provided information which could not be obtained by studying the polymer itself. Isomerism was proven by the nuclear magnetic resonance spectra of soluble ester-benzimidazole derivatives. This study indicated that a single band around 1755 cm^?1 should appear in the infrared spectrum of the completely cyclized polymer. The high melting points of the model imidazopyrrolones indicate the extreme thermal stability to be anticipated from perfectly formed pyrrone polymers.