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.