title: The reactions of diaminomaleonitrile with isocyanates and either aldehydes or ketones revisited.
abstract: A reinvestigation of the reactions of urea derivatives of diaminomaleonitrile 2 with aldehydes or ketones in the presence of triethylamine has established that the products of these reactions are not pyrimidino[5,4-d]pyrimidines 9 as previously reported, but 8-oxo-6-carboxamido-1,2-dihydropurines 12, which are oxidized rapidly in air to the corresponding 6-carboxamidopurines 13. Similarly, the reaction of Schiff base derivatives of DAMN 5 with isocyanates in the presence of triethylamine gives the substituted 2-oxoimidazoles 20 and not the pyrimidine derivatives 8 as previously claimed. The compounds 20 cyclize in solution and are easily oxidized to 8-oxopurine-6-carbonitriles 22, which give the same 8-oxopurine-6-carboxamides 13 upon further hydrolysis.
authors.affiliation: Departamento de Química, Universidade do Minho, Campus de Gualtar, 4710 Braga, Portugal.
authors.forename: B L
authors.initials: BL
authors.lastname: Booth
authors.forename: A M
authors.initials: AM
authors.lastname: Dias
authors.forename: M F
authors.initials: MF
authors.lastname: Proença
authors.forename: M E
authors.initials: ME
authors.lastname: Zaki