Abstract:

Pyrazolo[1,5-a]pyridine-3-carboxylate derivatives were obtained from 1,3-dipolar cycloaddition reaction with ethyl propionate and N-aminopyridine sulfates synthesized by the reactions of substituted pyridines and hydroxylamine-O-sulfonic acid. They were further treated with 30%NaOH aqueous solution to give corresponding substituted pyrazolo[1,5-a]pyridine-3-carboxylic acid derivatives. In this method, N-aminopyridine sulfates were directly put into the next reaction, which eliminated the step of converting sulfate into iodine salt in the traditional method and solved the problem that the iodine salt was difficult to precipitate. N-aminopyridine sulfate and ethyl propionate were dissolved in water and N,N-dimethylformamide, respectively, and then mixed to increase the solubility of reactants. Six compounds(4a~4f) were successfully synthesized with yields of 88%~93%. The method is mild, easy to process and low cost as a new process for mass production.

Key words: substituted pyridines, hydroxylamine-O-sulfonic acid, dipolar cycloaddition reaction, ethyl propionate, pyrazolo[1,5-a]pyridine-3-carboxylic acid