4-(Dimethylamino)Benzaldehyde → 5-(4-Dimethylamino-benzylamino)-2-methyl-phenol

To a solution of 4-dimethylaminobenzaldehyde 1 (14.8 g, 100 mmol) in methanol (250 mL) (Scheme 1) were added 5-amino-2-methyl-phenol 2 (14.8 g, 120 mmol) and sodium cyanoborohydride (19.0 g, 300 mmol). The reaction mixture was stirred at room temperature for 3 d. The reaction mixture was evaporated and water was added. The mixture was extracted with ethyl acetate, washed with brine and dried over MgSO4, filtered and evaporated to give a crude orange solid. This crude solid was recrystallized from hot ethyl acetate and hexane to yield 5-(4-dimethylamino-benzylamino)-2-methyl-phenol 3 as a tan solid (2.34 g, 9% yield): 1H NMR (400 MHz, DMSO-d6) δ 1.91 (s, 3H) 2.82 (s, 6H), 4.01 (d, J=5.5 Hz, 2H), 5.67 (s, 1H), 5.93 (d, J=7.5 Hz, 1H), 6.04 (s, 1H), 6.65 (m, 2H), 7.12 (d, J=8.2 Hz, 2H), 8.74 (s, 1H); 13C NMR (400 MHz, DMSO-d6) δ 15.6, 40.7, 46.6, 87.0, 99.9, 104.0, 111.1, 112.8, 128.3, 130.8, 148.4, 149.8, 156.0. To a solution of 3 (0.64 g, 2.5 mmol) in anhydrous THF (25 mL) were added 4-dimethylaminopyridine (0.31 g, 2.5 mmol) and di-tertbutyl dicarbonate (BOC2O) (2.18 g, 10 mmol). The reaction mixture was stirred at room temperature for 18 h. The solvent was evaporated and the residue was taken up into ethyl acetate (25 mL) and water (25 mL). The organic phase was washed with brine (25 mL), dried over MgSO4, filtered and evaporated to give a crude orange solid. This solid was recrystallized from hot ethanol and water to yield a carbonic acid tert-butyl ester compound 4 as a tan solid (1.17 g, 33% yield): 1H NMR (400 MHz, DMSO-d6) δ 1.45 (s, 9H), 1.91 (s, 3H), 2.88 (s, 6H), 4.06 (d, J=5.7 Hz, 2H), 6.03 (t, J=5.7 Hz, 1H), 6.28 (s, 1H), 6.38 (dd, J=2.0, 8.1 Hz, 1H), 6.66 (d,J=8.6 Hz, 2H), 6.88 (d, J=8.3 Hz, 1H), 7.14 (d, J=8.5 Hz, 2H); 13C NMR (400 MHz, DMSO-d6) δ 15.0, 27.6, 39.1, 46.5, 83.0, 105.9, 110.5, 112.8, 116.0, 127.6, 128.5, 131.3, 148.6, 149.9, 150.1, 151.4. To a solution of 4 (0.36 g, 1.0 mmol) in anhydrous THF (10 mL) was added di-tertbutyl dicarbonate (0.87 g, 4.0 mmol). The reaction mixture was stirred at 40° C. for 18 h. The solvent was evaporated and the residue was taken up into ethyl acetate (25 mL) and water (25 mL). The organic phase was washed with brine (10 mL), dried over MgSO4, filtered and evaporated to afford compound 5 as an orange oil (0.29 g, 62% yield): 1H NMR (400 MHz, DMSO-d6) δ 1.37 (s, 9H), 1.46 (s, 9H), 2.05 (s, 3H), 2.83 (s, 6H), 4.67 (s, 2H), 6.61 (d, J=8.3 Hz, 2H), 6.95 (m, 4H), 7.15 (d, J=7.7 Hz, 1H); 13C NMR (400 MHz, DMSO-d6) δ 14.7, 23.6, 26.8, 27.0, 27.5, 79.5, 82.8, 111.9, 123.6, 125.0, 126.4, 127.8, 130.1, 140.5, 145.9, 148.3, 149.2150.4, 153.4. To a solution of 5 (0.23 g, 0.49 mmol) in anhydrous DMF (5 mL) was added iodomethane (0.18 mL, 2.96 mmol). The reaction mixture was stirred at room temperature for 3 d. Diethyl ether (50 mL) was added, stirred overnight and decanted to yield compound 6 as an orange solid (137 mg, 47% yield): 1H NMR (400 MHz, DMSO-d6) δ 1.38 (s, 9H), 1.47 (s, 9H), 2.06 (s, 3H), 3.55 (s, 9H), 7.05 (dd, J=2.0, 8.1 Hz, 1H), 7.06 (s, 1H), 7.20 (d, J=8.3 Hz, 1H), 7.42 (d, J=8.9 Hz, 2H), 7.89 (d, J=7.9 Hz, 2H); 13C NMR (400 MHz, DMSO-d6) δ 15.4, 27.5, 28.2, 52.0, 56.7, 80.8, 83.6, 115.0, 119.9, 120.9, 123.0, 127.5, 128.5, 131.1, 134.0, 140.9, 146.0, 149.1, 151.1. The compound 6 (120 mg, 0.20 mmol) was dissolved in 4N hydrogen chloride in dioxane (0.5 mL, 2.0 mmol) and stirred at room temperature for 3 d. The solvent was evaporated and diethyl ether (5 mL) was added. The resulting precipitate was filtered to yield {4-[(3-hydroxy-4-methyl-phenylamino)-methyl]-phenyl}-trimethyl-ammonium chloride 7 as a dark orange solid (60 mg, 98% yield): 1H NMR (400 MHz, DMSO-d6) δ 1.94 (s, 3H), 3.56 (s, 9H), 4.30 (s, 2H), 6.06 (s, 1H), 6.20 (bs, 1H), 6.74 (m, 1H), 7.57 (d, J=8.6 Hz, 2H), 7.89 (d, J=8.9 Hz, 2H), 9.07 (s,1H); 13C NMR (400 MHz, DMSO-d6) δ 15.9, 56.7, 66.7, 110.0, 113.5, 120.7, 122.1, 131.2, 132.0, 128.0, 138.0, 157.0, 193.0; MS (M)+: 271.