To a solution of tert-butyl 6-amino-1,3,4,5-tetrahydro-2H-pyrido[4,3-b]indole-2-carboxylate (7 g, 24.3 mmol) in CH2Cl2 (40 mL) at rt was added saturated K2CO3 (30 mL), ethyl chloroformate (2.4 mL, 4.0 mmol) and stirred at 25° C. for 0.5 hour. The solution was diluted with water (30 mL) and extracted with CH2Cl2 (2×30 mL). The combined extracts were dried over magnesium sulfate, and concentrated to afford tert-butyl 6-[(ethoxycarbonyl)amino]-1,3,4,5-tetrahydro-2H-pyrido[4,3-b]indole-2-carboxylate (8.7 g, 100%) as an crude oil. MS [M+H]+360.
