3-Amino-1,2,3,4-tetrahydrocarbazol is prepared by the reaction of 1,4-dioxaspiro[4.5]decan-8-amine and phenylhydrazine. The specific synthesis steps are as follows: General procedure: Aqueous sulfuric acid solution (10 % w/v, 30 mL) was taken in a round bottom flask, added (1,4-dioxa-spiro[4.5]dec-8-yl)dimethylamine (12a, 1.5 g, 8.1 mmol) followed by phenylhydrazine (1.52 g, 14.08 mmol) at room temperature. The reaction mass was heated to reflux temperature (95-100 °C) and maintained reflux for 2-3 h. The progress of the reaction was monitored by TLC. After completion of reaction, the reaction mass was cooled to 10-15 °C. Then the mass was basified with aqueous sodium hydroxide solution (20 % w/v) and the aqueous layer was extracted with ethyl acetate. Organic layer was washed with brine solution, dried over anhydrous sodium sulfate and organic volatiles were removed by distillation under vacuum. The crude compound was purified by flash chromatography (ethyl acetate: triethylamine 9:0.2) to obtain 0.8 g of 3-Amino-1,2,3,4-tetrahydrocarbazol (13a), the yield being 50 %.
