New, convenient synthesis of 2‐alkyl‐ and 2‐vinylpyrazolo[3,4‐ d ]‐pyrimidine derivatives

Treatment of 1,3‐dimethyl‐6‐hydrazinouracil with the appropriate dimethylformamide dialkylacetal afforded the, corresponding 2‐alkyl‐5,7‐dimethylpyrazolo[3,4‐ d ]pyrimidine‐4,6‐(5 H ,7 H )diones. The reaction of 1,3‐dimethyl‐6‐(α‐methylbenzylidenehydrazino)uracils with dimethylformamide dimethylacetal or triethyl orthoformate gave the corresponding 5,7‐dimethyl‐2‐vinylpyrazolo[3,4‐ d ]pyrimidine‐4,6(5 H ,7 H )diones, respectively. Similarly, treatment of 1,3‐dimethyl‐6‐(α‐methylbenzylidenehydrazino)uraeils with triethyl orthopropionate yielded the corresponding 5,7‐dimethyl‐3‐ethyl‐2‐vinylpyrazolo[3,4‐ d ]pyrimidine‐4,6(5 H ,7 H )diones.