To a stirred solution of 2,8-dimethyl-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole (0.14 g, 0.00070 mol) and copper sulfate (0.017 g, 0.00007 mol) in toluene (4 mL) was added potassium carbonate (0.193 g, 0.0014 mol) and 1,10-phenanthroline (0.025 g, 0.000014 mol). The reaction mixture was stirred for 5 min at RT. A solution of 5-(bromoethynyl)-2-methylpyridine (0.150 g, 0.00077 mol) in toluene (2 mL) was added to the reaction mixture. After addition, the reaction mixture was stirred for 12 h at 80° C. After completion of reaction (monitored by TLC), solvent was removed under reduced pressure, and the crude product was purified by column chromatography (4% MeOH:DCM as eluent on silica (100-200 mesh), diameter of column—5.0 cm, height of silica—approx. 5 inch). The product was further purified by preparative TLC to give the desired compound as a yellow colored oil (0.010 g, 4.5% yield). 2,8-Dimethyl-5-((6-methylpyridin-3-yl)ethynyl)-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole (0.01 g, 0.0000317 mol) was dissolved in THF (1.0 mL). A solution of oxalic acid dihydrate (0.004 g, 0.0000317 mol) in THF (1 mL) was added and stirred for 30 min at RT. The precipitate was filtered and dried to give the oxalate salt as a white solid (0.006 g, 46.8% yield). 1H NMR (DMSO, oxalate salt) δ (ppm): 8.70 (s, 1H), 7.90 (d, 1H), 7.60 (d, 1H), 7.38 (d, 2H), 7.18 (d, 1H), 4.20 (m, 2H), 3.40 (m, 2H), 3.10 (m, 2H), 2.80 (s, 3H), 2.50 (s, 3H), 2.40 (s, 3H).
