Acetic Acid → 4-Bromo-6-fluoro-1H-indole

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To a solution of 1-bromo-5-fluoro-2-methyl-3-nitrobenzene (4.69 g, 20 mmol) in 1,4-dioxane (25 mL) at RT was slowly added DMF dimethylacetal (13.3 mL) and pyrrolidine (1.7 mL). The solution was heated at 100° C. for 18 h, then concentrated in vacuo to give a dark residue. To the residue was added HOAc (30 mL) and iron powder (11 g, 200 mmol) then the mixture was heated to reflux for 1 h, cooled to RT, neutralized by addition of 50% aq. NaOH and extracted with EtOAc (2×200 mL). The combined organic extracts were dried (MgSO4), filtered and concentrated in vacuo. The residue was purified by SiO2 chromatography eluting with an EtOAc/petroleum ether gradient (5 to 30% EtOAc) to afford 1.16 g (27%) of 4-bromo-6-fluoro-1H-indole (224)—as brown solid: MS (ESI) m/z=213.9 [M+1]+.

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