α,β-Unsaturated Carboxylic Acid Derivatives. IV. General Synthesis of Unsaturated Unsymmetric 3,6-Disubstituted-2,5-piperazinediones

A general synthetic route to unsymmetric 3,6-dialkylidene and 3-alkylidene-6-arylidene-2,5-piperazinediones is described. The condensation reaction of ethyl 2-oxocarboxylates with chloroacetamide in the presence of several acidic catalysts afforded N-chloroacetyldehydroamino acid esters. These compounds were cyclized in saturated ethanolic ammonia to give 3-monoalkylidene and benzylidene-2,5-piperazinediones (2). Compound 2 and 1-monoacetyl- or 1,4-diacetyl-3-alkylidene and benzylidene-2,5-piperazinediones, derived from a reaction of 2 with acetic anhydride, were condensed with alkyl and arylaldehyde in the presence of bases to afford 5.