The synthesis of 4‐ and 6‐substituted 1‐H‐ and 1‐phenyl‐pyrazolo‐(3,4‐d)‐pyrimidines is described. It starts from ethyl ethoxymethylene cyanoacetate from which the 4‐hydroxy‐pyrazolo‐(3,4‐d)‐ pyrimidines can be obtained in two steps through the corresponding 2‐substituted 3‐amino‐4‐carbethoxy‐pyrazoles.
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Schmidt et al. (1956) studied this question.
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