3,3,5-Tribromo-1H-pyrrolo[2,3-b]pyridin-2(3H)-one → 5-bromo-1H,2H,3H-pyrrolo(2,3-b)pyridin-2-one

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Reaction Conditions

Reaction Steps

Zinc dust (34.0 g, 0.52 mol) was added in small portion to a stirred suspension of 3 (40.85 g, 0.111 mol) in glacial acetic acid (1000 mL) at such a rate that the temperature was maintained between 20-25° C. (strongly exothermic reaction; external ice bath cooling). Addition took about 20 min. Cooling bath was removed and stirring was continued at r.t. for 2 h. The solid was filtered off, washed with toluene (50 mL) and triturated with CH2Cl2:MeOH=4:1 (2.5 L). The solution was decanted off and treated with 1.0 M aqueous Na2CO3 solution (170 mL). After stirring for 1 h the two layers were separated. The organic layer was washed again with 1.0 M aqueous Na2CO3 solution (50 mL). The combined aqueous layers were extracted with CH2Cl2:MeOH=4:1 (10×100 mL). Combined organic solutions were dried with MgSO4 (200 g) and concentrated. The residual solid was dissolved in THF (2000 mL) and insoluble material was filtered off. The filtrate was concentrated to dryness in vacuum to afford 4 (16.93 g, 72%) as tan solid. 1H NMR (400 MHz, DMSO-d6) δ 3.57 (s, 2H), 7.75 (m, 1H), 8.14 (m, 1H), 11.13 (bs, 1H).

Provenance & Evidence