Differentiation of regioisomeric N-alkylation of some indazoles and pyrazolopyridines by advanced NMR techniques

Indazole scaffold have two interconvertible tautomeric forms. Regioselectivities were determined for N-benzylations and alkylation of some non-substituted and substituted indazoles, under basic conditions (K₂CO₃) in DMF. The ratio of regioisomers occurrence between N¹:N² is almost equal. Their structures were established through a combination of NOESY and ¹H-¹³C/¹⁵N HMBC NMR methods. Additionally, pyrazolo[3,4-b]pyridines have also three possible tautomeric forms; primarily 1H and 2H, with 7H isomers being rare. Pyrazolo[4,3-b]pyridines have only known two possible tautomeric forms so far; 1H and 2H.