Pyrazolo[3,4-b]pyridines: Syntheses, reactions, and nuclear magnetic resonance spectra

Efficient syntheses of approximately 70 simple substituted representatives of pyrazolo[3,4-b]pyridine 1 are reported from the following: (a) suitably substituted pyridines onto which a pyrazole ring is annelated, and (b) appropriately substituted pyrazoles onto which a pyridine ring is annelated. Selected examples of electrophilic, nucleophilic, and homolytic substitution reactions and group transformations are described, providing regiosynthetic paths to useful intermediate species. Some systematic aspects of substituent chemical shift influences in the 1H and 13C nuclear magnetic resonance spectra, aiding in structural assignments, are illustrated.