Isomerization of pirazolopyrimidines to pyrazolopyridines by ring-opening/closing reaction in aqueous NaOH†

An isomerization reaction of 7-aryl-3-formylpyrazolo[1,5-a]pyrimidines to 5-aroyl-NH-pyrazolo[3,4-b]pyridines proceeding with high yields in aqueous NaOH under microwave conditions is reported. This unprecedented transformation occurs by adding and eliminating a water molecule via an ANRORC mechanism (adding the nucleophile, ring-opening, and ring-closing) studied using DFT calculations. The product's utility was proved as they have aroyl and NH groups that simple methods and readily available reagents easily modified; likewise, their optical properties were studied, highlighting their high potential as highly emissive modular dyes (φ_F up to 99%). NMR, HRMS, and X-ray diffraction analysis resolved the products' structures.