Hydrochloric Acid → tert-butyl 7-bromo-1,3,4,5-tetrahydro-2H-pyrido[4,3-b]indole-2-carboxylate

Participants

Reaction Steps

3-Bromophenylhydrazine (40.0 g, 0.179 mol) and N-Boc-4-oxo-piperidine (35.4 g, 0.179 mol) were dissolved in ethanol (368 mL), and conc. HCl (72 mL) was added. The reaction mixture was then heated to reflux for 18 h, concentrated and basified using 10% NH4OH in methanol (10%, 100 mL). The solvent was removed, and the residue was suspended in CH2Cl2 (1.2 L). Boc2O (39.2 g, 0.179 mol) followed by DMAP (195 mg, 1.6 mmol) and triethylamine (46.4 mL, 0.358 mol) were then added, and the reaction progressed at room temperature for 18 h. The mixture was washed with 0.5 N HCl, and the organic phase was removed, dried over Na2SO4, filtered and concentrated to dryness. The resulting mixture of regioisomers was purified by flash column chromatography (silica gel, hexanes/EtOAc, 100:0 to 80:20 to 50:50 then 25:75) to give the more polar title compound (26.2 g, 42%) as a yellow solid: 1H NMR (300 MHz, CDCl3) δ 8.16 (br s, 1H), 7.42 (s, 1H), 7.28 (d, J=8.1 Hz, 1H, partially masked by solvent), 7.18 (d, J=8.1 Hz, 1H), 4.60 (s, 2H), 3.80 (t, J=5.5 Hz, 2H), 2.79 (t, J=5.6 Hz, 2H), 1.51 (s, 9H).

Provenance & Evidence