N-Boc-protected 5-formyl-1H-pyrazol-4-amines react with malonic acid in pyridine in the presence of pyrrolidine at 45–50°С or with malonic acid monomethyl ether in the presence of pyrrolidine in AcOH under reflux with the formation of 5-oxo-4,5-dihydro-1H-pyrazolo[4,3-b]pyridine-6-carboxylic acids. The reaction of N-Boc-protected 5-formyl-1H-pyrazol-4-amines with cyanoacetic acid in pyridine in the presence of pyrrolidine at 45–50°С leads to the formation of 5-oxo-4,5-dihydro-1H-pyrazolo[4,3-b]pyridine-6-carbonitriles. The latter can also be obtained via cyclocondensation of N-Boc-protected 5-formyl-1H-pyrazol-4-amines with methyl cyanoacetate in AcOH under reflux in the presence of pyrrolidine or in MeCN containing pyrrolidine and a catalytic amount of proline heated under reflux.
