The title compounds (2a-d) representing α,β-didehydroalanine derivatives and reactive equivalents of pyruvic acid, have been obtained by the reaction of methyl or tert-butyl pyruvate with dimethylamine, piperidine or morpholine in the presence of arsenous trichloride.The synthesis of dimethyl 2,4-dioxopentanedioate is given as an example of the versatile reactivity of these compounds.