Synthesis of pyrazolo[3,4‐<i>d</i>]pyrimidine derivatives using ketene dithioacetals

Abstract

Abstract The cyclization of 5‐amino‐3‐methylthiopyrazole‐4‐carbonitriles or 4‐carboxamides 3a‐j , which were prepared by the reaction of ketene dithioacetals 1a,b [1a : bis(methylthiomethylenemalononitrile; 1b : bis(methylthio)methylenecyanoacetamide] with hydrazines (hydrazine hydrate, phenylhydrazine, p ‐chlorophenylhydrazine, p ‐nitrophenylhydrazine), with formamide or carbon disulfide proceeded to give the corresponding 4‐amino‐ or 4‐hydroxy‐3‐methylthiopyrazolo[3,4‐ d ]pyrimidines 6a‐h in good yields. 3‐Aminopyrazolo[3,4‐ d ]pyrimidine derivatives 6i‐1 were also obtained by the application of the cyclization reaction of 3,5‐diaminopyrazoles with formamide.