Reaction Steps
Trifluoroacetic acid (1 mL) was added to a stirred solution of 2-tert-butoxycarbonyl-7-(methylthio)-1,2,3,4,10,10a-hexahydropyrazino[1,2-a]indole (70 mg, 0.21 mmol) in dichloromethane. (5 mL) at room temperature under Ar. The reaction was stirred at room temperature for 1 h then poured into saturated aqueous sodium hydrogen carbonate solution (50 mL) and extracted with dichloromethane (3×30 mL). The combined organic extracts, were washed with brine (1×30 mL), dried (magnesium sulfate), filtered and the solvent removed under vacuum to leave a crude oil. The oil was dissolved in 2-propanol (5 mL) and heated to reflux. Fumaric acid (1 eq) was added and the solution was cooled to room temperature. The emerging precipitate was filtered, washed with ether and dried to give the product as a white solid (40 mg, 54%). mp 196–198° C. Found: C, 56.50; H, 5.89; N, 8.15%. C12H16N2S. 1.1 C4H4O4 requires: C, 56.60; H, 5.91; N, 8.05%. IR νmax (Nujol)/cm−1 3595, 3188, 2925, 2854, 2457, 1696, 1585, 1485, 1486, 1461, 1402, 1377, 1345, 1317, 1279, 1230, 1179, 1154, 1129, 1066, 1058, 1005, 996, 972, 919, 987, 868, 835, 797, 722, 644, 606, 547 and 482: NMR δH (400 MHz; DMSO-d6) 6.99 (1H, d, J 7.5 Hz), 6.52 (2H, s), 6.47–6.51 (2H, m), 3.69–3.72 (1H, m), 3.50–3.62 (2H, m), 3.05–3.20 (3H, m), 2.91–3.02 (2H, m), 2.65–2.80 (2H, m), 2.43 (3H, s).
