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

• DOI: 10.1021/acs.joc.6b02431
• Publication Date: 2016-11-28T12:07:49Z
• Authors: Juan-Carlos Castillo; Diego Estupiñan; Manuel Nogueras; Justo Cobo; Jaime Portilla
• Keywords: Purine metabolism; Atom economy

A microwave-assisted approach for the regioselective synthesis of functionalized 6-(aryldiazenyl)pyrazolo[1,5-a]pyrimidin-7-amines from cyclization 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 versatile palladium-catalyzed reductive azo cleavage is disclosed diverse heteroaromatic 1,2-diamines, a valuable synthetic building block to develop new fused systems. As example, several substituted pyrazolo[5,1-b]purines were synthesized in yields up 96% using microwave irradiation cyclocondensation these 1,2-diamines orthoesters.