Synthesis of 2-methyl-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole (17): phenylhydrazine (1.0 g, 9.3 mmol) and N-methyl-4-piperidone (1.1 g, 9.3 mmol) were dissolved in 1,4-dioxane (35 mL) and the mixture was cooled down to 0 °C. Concentrated sulfuric acid (5 mL) was slowly added dropwise at 0 °C and under stirring conditions, and a precipitate was generated during the reaction. Subsequently, the reaction mixture was heated to 60 °C and maintained for 1 hour until the precipitate was completely dissolved. The reaction mixture was continued to be stirred at 60°C for 1 hour. Upon completion of the reaction, the mixture was cooled to room temperature and the pH was adjusted to about 12 by addition of saturated aqueous sodium bicarbonate, assisted by addition of a small amount of solid sodium hydroxide if necessary. The organic product was extracted with chloroform (3 x 20 mL), the organic phases were combined and washed with brine (15 mL), dried over anhydrous sodium sulfate and concentrated under reduced pressure. Purification by column chromatography (elution gradient: hexane solution of 0-80% ethyl acetate) afforded the target product (1.6 g, 93% yield) as a beige solid.1H NMR (400 MHz, DMSO-d6): δ 10.80 (s, 1H), 7.30 (m, 2H), 6.98 (m, 2H), 3.53 (s, 2H), 2.79 (t, J = 5.2 Hz, 2H), 2.71 (t, J = 5.4 Hz, 2H), 2.43 (s, 3H).13C NMR APT (100 MHz, CDCl3): δ 136.2 (CH), 132.0 (CH), 126.0 (CH), 121.0 (CH2), 119.1 (CH2), 117.4 (CH2), 110.7 (CH2), 117.4 (CH2), 117.4 (CH2), 117.4 (CH2), 117.4 (CH2), 117.4 (CH2), 117.4 (CH2) 110.7 (CH2), 108.3 (CH), 52.5 (CH2), 51.8 (CH2), 45.8 (CH3), 23.5 (CH2) ESI-HRMS (m/z): [M + H]+ Calculated value C12H14N2, 187.1230; measured value, 187.1228.
![2-methyl-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole](/CAS/GIF/5094-12-2.gif)