Para‐Toluenesulfonic Acid‐Catalyzed Green Synthesis of Pyrazolo[1,5‐a]pyrimidines from 5‐Aminopyrazoles and Terminal Keto‐Alkynes

A simple and effective approach has been established for the synthesis of novel multi‐substituted pyrazolo[1,5‐ a ]pyrimidine derivatives utilizing 5‐amino‐pyrazoles and terminal keto‐alkynes as starting materials. This method achieves excellent yields under catalytic acidic conditions in environmentally benign solvents (water/ethanol) at ambient temperature. Moreover, this protocol affords NMR pure products through a simple filtration process. Additionally, the synthetic utility is validated through a gram‐scale synthesis of the biologically active tubulin inhibitor, 6 . Thereby emphasizing the pivotal role of chemistry in designing and producing potent anticancer molecules for therapeutic use.