4’-Ethyl 1,2-dimethyl 1’,5-dibenzyl-4,4-dicyano-2’-oxo-5’-phenyl-1’,2’,4a,5-tetrahydro-4H-spiro[benzo[4,5]imidazo[1,2-a]pyridine-3,3’-pyrrole]-1,2,4’-tricarboxylate

The 1,4-dipolar cycloaddition of the ylidene derivative of 1H-pyrrole-2,3-dione to a dipole generated in situ from 1-benzylbenzimidazole and dimethyl acetylenedicarboxylate proceeds via the exocyclic multiple bond of the ylidene derivative and affords a mixture of diastereomeric spiro[benzo[4,5]imidazo[1,2-a]pyridine-3,3’-pyrroles], which slowly epimerized in a solution.