Synthesis of Tetrahydrocarbazole Derivatives Using Thiamine Hydrochloride (VB₁) as Efficient Catalyst

The tetrahydrocarbazole derivatives are widely used in pharmaceutical chemistry.A simple and highly efficient method was developed for the construction of tetrahydrocarbazole derivatives from phenylhydrazine hydrochloride and cyclohexanone in the presence of thiamine hydrochloride (VB₁) in ethanol.This protocol relies on the use of various cyclohexanone and phenylhydrazine hydrochloride with electron-donating and electron-withdrawing groups to access tetrahydrocarbazole scaffolds with a wide scope.Most of the target products catalyzed by VB₁ were obtained in good to excellent yields (>90%).VB₁ acted as an efficient,mild and non-toxic catalyst in the reaction,and it could be reused without reducing the catalytic efficiency.