Synthesis of Ethyl 4(1H)‐Oxopyrimido[1,2‐a]perimidine‐3‐carboxylate

In a recent communication1), we reported the synthesis of some biologically interesting 1‐substituted 3‐(2‐perimidyl)‐ ureas starting from 2‐aminoperimidine (1a). Because of the presence of a 1,3‐dinucleophilic center in this molecule, 1a might undergo cyclocondensation with appropriate dielectrophiles. So this compound might be a useful synthon for the generation of novel fused perimidine derivatives. In an orientation experiment, we found that the reaction of 1a HBr with dimethyl acetylenedicarboxylate in the presence of Et3N proceeded smoothly and afforded methyl 4(1H)‐oxopyrimido[1,2‐a]perimidine‐2‐carboxylate 2a in 52% yield2). The structure ov 2a was assigned on the basis of spectral analysis.