Facile synthesis of 6-cyano-9-substituted-9H-purines and their ring expansion to 8-(arylamino)-4-imino-3-methylpyrimidino[5,4-d]pyrimidines

6-Cyano-9-substituted-9H-purines were prepared in a high yielding, one-step process by refluxing triethyl orthoformate or triethyl orthopropionate with the corresponding (Z)-N1-(aryl- or benzyl)-N2-(2-amino-1,2-dicyanovinyl)formamidines. Attempted reaction of these cyanopurines with aqueous methylamine furnished 8-(arylamino)-4-imino-3-methylpyrimidino[5,4-d]pyrimidines, by attack at the imidazole ring rather than addition to the 6-cyano group. All compounds have been fully characterised by spectroscopic data and an X-ray crystal structure determination has been carried out on the 8-(4-methoxyanilino)-4-imino-3-methylpyrimidino[5,4-d]pyrimidine.