116650-33-0

97096-16-7

100-63-0

61894-99-3

A 10% (w/v) aqueous sulfuric acid solution (30 mL) was added to a round-bottomed flask followed by (1,4-dioxaspiro[4.5]dec-8-yl)dimethylamine (12a, 1.5 g, 8.1 mmol). Phenylhydrazine (1.52 g, 14.08 mmol) was added dropwise to the mixture at room temperature. The reaction mixture was heated to reflux temperature (95-100°C) and maintained at reflux for 2-3 hours. The reaction process was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the reaction mixture was cooled to 10-15°C. Subsequently, the mixture was alkalized with 20% (w/v) aqueous sodium hydroxide solution and the aqueous layer was extracted with ethyl acetate. The organic layer was washed with saturated brine and dried with anhydrous sodium sulfate. Subsequently, the organic solvent was removed by distillation under reduced pressure. The crude product was purified by fast column chromatography (eluent: ethyl acetate/triethylamine = 9:0.2) to afford (R)-2,3,4,9-tetrahydro-1H-carbazol-3-amine (13a, 0.8 g) in 50% yield.