Heterocyclic aldehyde synthesis, acetic anhydride

Piperazinedione condenses easily with benzaldehyde in the presence of acetic anhydride/sodium acetate to yield 3,6-dibenzylidene-2,5-piperazinedione (343, 344). Analogous preparations have been conducted with heterocyclic and unsaturated aliphatic aldehydes (19), but not with saturated aliphatic aldehydes. The synthesis of alkylidenepiperazine-diones can be realized by condensation of N,N -diacetylpiperazine-diones with aliphatic aldehydes in the presence of potassium t-butoxide (138, 140), conditions also applicable to the synthesis of monoarylidene-piperazinediones. A second condensation is however only possible with aromatic aldehydes. 

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