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0 °C

An ice cold mixture of ethyl 9-cyclopropyl-4-hydroxy-2-methyl-6,7,8,9-tetrahydro-5H-pyrido[2,3-b]indole-3-carboxylate (1.362 g, 4.33 mmol) in dichloromethane (DCM) (20 ml) was treated with Et3N (0.906 ml, 6.50 mmol) and Tf2O (0.805 ml, 4.77 mmol), and then stirred at 0° C. for 90 min. The mixture was concentrated and purified with column chromatography (0-50% EtOAc/Hexane, 120 g silica gel) to give ethyl 9-cyclopropyl-2-methyl-4-(((trifluoromethyl)sulfonyl)oxy)-6,7,8,9-tetrahydro-5H-pyrido[2,3-b]indole-3-carboxylate (1.8341 g, 4.11 mmol, 95% yield) as white solid. 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 4.39 (q, J=7.2 Hz, 2 H), 3.17-2.98 (m, 1 H), 2.90-2.78 (m, 4 H), 2.75 (s, 3 H), 1.99-1.88 (m, 2 H), 1.88-1.76 (m, 2 H), 1.40 (t, J=7.2 Hz, 3 H), 1.22-1.07 (m, 4 H); LCMS (m/z) ES+=447 (M+1).

1. concentrationThe mixture was concentrated
2. custompurified with column chromatography (0-50% EtOAc/Hexane, 120 g silica gel)