Trifluoroacetic acid → 6-Bromo-8-fluoro-3,4-dihydro-2H-pyrazino[1,2-a]indol-1-one

Participants

Reaction Conditions

Reaction Steps

To a stirred solution of ethyl 7-bromo-1-(2-(tert-butoxycarbonylamino)ethyl)-5-fluoro-1H-indole-2-carboxylate (step A) (1.43 g, 3.33 mmol) in dichloromethane (15.2 ml) was added drop wise at 0° C. trifluoroacetic acid (4.79 g, 3.23 ml, 42.0 mmol). Afterwards the solution was allowed to stir for 15 min at 0° C., and for 30 min at room temperature. The reaction mixture was evaporated and the remaining material was solved in methanol (15.2 ml). Potassium carbonate (1.83 g, 13.3 mmol) was added and the mixture was allowed to stir at room temperature for 17 h. The mixture was evaporated, water (50 ml) was added and the mixture was extracted with dichloromethane (2×40 ml). The combined organic layers were washed with brine (50 ml), dried (MgSO4) and evaporated. The crude product (0.86 g) was purified by trituration with dichloromethane (3 ml) and heptane (15 ml) to yield the title compound as an off-white solid (0.85 g, 90%), MS (ISN) m/z=283.2 [(M+H)+], mp 253.5° C.

Provenance & Evidence