Convenient Synthesis of New N-3-Substituted Pyrido[1′,2′:1,5]pyrazolo[3,4-d]pyrimidine-2,4(1H,3H)-dione Derivatives

Previously unknown N-3-substituted pyrido[1′,2′:1,5]py­razo­lo[3,4- d ]pyrimidine derivatives were synthesized by a straightforward four-step synthesis. Starting from a 1-aminopyridinium salt, dimethyl acetylenedicarboxylate condensation followed by a fully regioselective saponification led to a pyrazolo[1,5- a ]pyridine monoester as a key intermediate. A Curtius rearrangement directly followed by amine condensation afforded a urea library. A final pyrimidine ring closure resulted in achievement of the heterocyclic construction. This straightforward strategy provides an efficient method to easily access a library of rare tricyclic scaffolds and highly valuable derivatives.