How is 4,5,6,7-Tetrahydro-1H-indazole hydrochloride (CAS: 18161-11-0) typically synthesized?

4,5,6,7-Tetrahydro-1H-indazole hydrochloride is typically synthesized from indole or 1H-indazole using electrophilic aromatic substitution followed by N-substitution with a chloride source. The reaction is usually conducted in an inert solvent like dichloromethane or tetrahydrofuran, with a Lewis acid catalyst such as aluminum chloride. Yields are generally high, and the reaction is selective and reproducible.