To a solution of 8-Ethyl-2-methyl-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole (0.1 g, 0.00046 mol) in N-methyl 2-pyrolidone (1.0 mL) was added powdered potassium hydroxide (0.13 g, 0.0023 mol) and allowed to stir for 10 min at RT. 2-methyl-5-vinyl pyrimidine (0.14 g, 0.00116 mol) was added and stirred for further 3 h. At 80 deg C. After completion (TLC), reaction mixture was diluted with water (15 mL) and extracted with ethyl acetate (3×50 mL). The organic layer was dried over anhydrous sodium sulphate and concentrated under reduced pressure using rotary evaporator. The crude was purified through column chromatography (7% MeOH:DCM in silica 100-200 mesh, Diameter of column—2.5 cm, Height of silica—approx. 5 inch) then purified through preparative TLC. to get the desired compound as yellow oil (0.032 g, 20% yield). 8-Ethyl-2-methyl-5-[2-(2-methyl-pyrimidin-5-yl)-ethyl]-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole (0.032 g, 0.000095 mol) was dissolved in THF (1.0 mL). A solution of oxalic acid dihydrate (0.012 g, 0.000095 mol) in THF (1.0 mL) was added and stirred for 30 min at RT, Precipitate obtained was filtered and dried to give oxalate salt as off white solid (0.030 g, 75% yield).
