The reaction of the lithium enolate of 1-benzyl-5-oxo-3-pyrrolidinecarboxylic acid 3 with a series of b-aryl, beta-nitroenamines unexpectedly afforded 6-aryl-2-benzyl-4-oxa-1-oxo-3a-methoxycarbonyl-2,5-diazaindenes 9a–d, whose structure was determined by analytical and NMR spectroscopical analysis. The structure of 9b was further confirmed by X-ray analysis. A reasonable mechanism for their formation is given
