Unexpected Aldehyde-Catalyzed Reaction of Imidazole N-Oxides with Ethyl Cyanoacetate

The reaction of 2-unsubstituted imidazole N-oxides with ethyl cyanoacetate and aromatic aldehydes leads to the formation of ethyl 2-cyano-2-(1,3-dihydro-2H-imidazole-2-ylidene)acetates. The reaction proceeds through an initial [3+2] cycloaddition, followed by cleavage of the cycloadduct and regeneration of the aldehyde, which essentially plays a catalytic role.