The reactions of diaminomaleonitrile with isocyanates and either aldehydesor ketones revisited

A reinvestigation of the reactions of urea derivatives of diaminomaleonitri le 2 with aldehydes or ketones in the presence of triethylamine has establi shed that the products of these reactions are not pyrimidino[5,4-d]pyrimidi nes 9 as previously reported, but 8-oxo-6-carboxamido-1,2-dihydropurines 12 which are oxidized rapidly in air to the corresponding 6-carboxamidopurine s 13. Similarly, the reaction of Schiff base derivatives of DAMN 5 with iso cyanates in the presence of triethylamine gives the substituted 2-oxoimidaz oles 20 and not the pyrimidine derivatives 8 as previously claimed. The com pounds 20 cyclize in solution and are easily oxidized to 8-oxopurine-6-carb onitriles 22, which give the same 8-oxopurine-6-carboxamides 13 upon furthe r hydrolysis.