6‑(Aryldiazenyl)pyrazolo[1,5‑a]pyrimidines as Strategic Intermediates for the Synthesis of Pyrazolo[5,1‑b]purines

A microwave-assisted approach for the regioselective synthesis of functionalized 6-(aryldiazenyl)­pyrazolo­[1,5-a]­pyrimidin-7-amines from the cyclization of 3-oxo-2-(2-arylhydrazinylidene)­butanenitriles with 5-amino-1H-pyrazoles under solvent-free conditions has been developed. This methodology was distinguished by its broad substrate scope, operational simplicity, high atom economy, and high-yielding without requiring chromatographic purification. In addition, an efficient and versatile palladium-catalyzed reductive azo cleavage is disclosed for the synthesis of diverse heteroaromatic 1,2-diamines, a valuable synthetic building block to develop new fused heteroaromatic systems. As synthetic example, several substituted pyrazolo­[5,1-b]­purines were synthesized in yields up to 96% by using microwave irradiation in the cyclocondensation of these 1,2-diamines with orthoesters.