Ammonia → 4-Fluoro-1H-indole-7-carbonitrile

Participants

Reaction Steps

Intermediate 1 was prepared according to procedures described in Wallace, O. B. et al. PCT int. appl. WO0204440, and as described in Steps A-D below. Step A A mixture of 4-fluoro-7-bromoindole (600 mg, 2.8 mmol) and CuCN (1.004 g, 11.2 mmol) in DMF (4 ml) was refluxed for 16 hours. After cooling to room temperature, the reaction mixture was poured into a solution of ammonia in MeOH (30 ml, sat.) and the residue removed by filtration. The filtrate was added to a mixture of water (20 ml)/ammonia (20 ml, sat. aq.) and extracted with EtOAc/Ether (1/1) until TLC analysis showed no product in the aqueous phase. The combined organic extracts were washed with brine (2×200 ml) and water (200 ml), dried (MgSO4); evaporation in vacuo gave 4-fluoro-7-cyanoindole as a tan yellow solid (310 mg, 69%). Step B To a solution of KOH (13.04 g, 0.232 mol) in 14% H2O/EtOH (50 ml) was added 4-fluoro-7-cyanoindole (900 mg, 5.60 mmol). The resulting mixture was refluxed for 12 hours, slowly cooled to room temperature, and concentrated in vacuo to about 30 ml. The residue was acidified to pH 2 with HCl (˜5.5 N aq.). The precipitate was filtered, washed with excess of water, and dried under high vacuum to afford 4-fluoro-7-carboxyindole as a white solid (100% conversion). The material was used without further purification. Step C To a suspension of 4-fluoro-7-carboxyindole in a mixture of MeOH (18 ml)/PhH (62 ml) was added (trimethylsilyl)diazomethane (8.8 ml, 17.6 mmol, 2 M in hexane). The resulting mixture was stirred at room temperature for 30 min., quenched with excess acetic acid and evaporated in vacuo. The crude oily material was purified by flash chromatography using a gradient elution (Hexane to 10% EtOAc/Hexane) to afford 4-fluoro-7-carbomethoxy indole as a white solid (1.04 g, 83% two steps). Step D

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