DMF acetals as alkylating and cyclizing agents: A facile route to substituted pyrazolo{[}3,4-d]pyrimidine-4,6(5H,7H)-diones

Several 7-methyl-5-alkyl-2-vinylpyrazolo{[}3,4-d]pyrimidine-4,6(5H,7H)-diones were prepared. The successful cyclization and alkylation of 6-(alpha-methylbenzylidenehydrazino)-1-methyluracils 2a-d using dimethylformamide acetals at high temperature provided 6a-d, 7a-d, and 8a-d. Treatment of 6a-d and 7a-d with acid afforded 7-methyl-5-alkylpyrazolo{[}3,4-d]pyrimidine-4,6(5H,7H)-diones 9a, b; under the same conditions, 3a-d reacted to 7-methylpyrazolo{[}3,4-d]pyrimidine-4,6(5H)-dione (4) in good yield.