A rapid and direct access to symmetrical/unsymmetrical 3,4-diarylmaleimides and pyrrolin-2-ones

1,8-Diazabicyclo5.4.0]undec-7ene (DBU) facilitated the oxidative cyclization of phenacyl amide in the presence of atmospheric oxygen under environmentally friendly conditions. The reaction has been studied under various conditions and a plausible mechanism is proposed. This ‘green’ reaction proceeds via intramolecular ring closure of the amide followed by subsequent reaction with molecular oxygen where DBU played a crucial role. A variety of phenacyl amides were treated with DBU in acetonitrile under an oxygen atmosphere to give the symmetrical/unsymmetrical 3,4-diarylsubstituted maleimides in good yields. Corresponding pyrrolin-2-ones however, were obtained in good to excellent yields when K₂CO₃ was used in place of DBU affording a practical synthesis of these compounds of potential biological interest.