Reactions Of Heterocyclic Ketene Aminals With Dimethyl Oxalate: A Facile Synthesis Of Gamma-Lactam Fused 1,3-Diazaheterocycles

Heterocyclic ketene aminals 1 or 2 react with dimethyl oxalate at room temperature in the presence of sodium hydride to produce the gamma-lactam fused 1,3-diazaheterocycles, 7-aroyl-2,3-dihydro-6-hydroxy-5H-pyrrolo[1,2-a]imidazol-5-ones 3 or 8-aroyl-2,3,4,5-tetrahydro-7-hydroxy-6H-pyrrolo[1,2-a]pyrimidin-6-ones 4, respectively, in good yields. A reasonable mechanism which involves N-acylation and intramolecular condensation steps was proposed. Under similar conditions, 1 and ethyl formate reacted to form only the N-formylation products, 2-(aroylmethylene)-1-formylimidazolidines 5, in high yields.