A mild approach to the synthesis of 4-Amino-8-(arylamino)pyrimido[5,4-d]pyrimidine 3-Oxides

The reaction of benzylhydroxylamine with 6-cyanopurines leads to the formation of 7-benzyloxy-8-imino-7,8-dihydropyrimido[5,4-d]pyrimidines. The hydrochloride of these compounds, isolated upon addition of aqueous hydrochloric acid, is a convenient precursor of the pyrimido[5,4-d]pyrimidine N-oxides when a suspension of the salt is refluxed in ethanol or acetonitrile. Refluxing a solution of the same salt in ethanol, leads to the Dimroth-rearranged product.The authors gratfully acknowledge the financial support by Universidade do Minho, Centro de Quimica and Funda Ao para a Ciencia e Tecnologia (FTC) (project PPCDT/QUI/59356/2004 and PhD grant to A. R. SFRH/BD/24760/2005)