2-Ethoxymethylene-3-oxobutanenitrile is a versatile trifunctional reagent that allows the introduction of a three-carbon moiety to amine-substrates. The reaction of the title compound with hydrazines has been studied leading to appropriate substituted pyrazoles 4–11. Reactions with other dinitrogen nucleophiles were studied giving access to a set of fused pyrimidines 13. All types of compounds displayed