2,3-Dichloro-5,6-dicyano-1,4-benzoquinone → ethyl 5-bromo-8-carbamoyl-9H-carbazole-2-carboxylate

Participants

Reaction Steps

A stirred suspension of ethyl 5-bromo-8-carbamoyl-2,3,4,9-tetrahydro-1H-carbazole-2-carboxylate (Intermediate 47-1, 9.31 g, 25.5 mmol) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (12.73 g, 56.1 mmol) in toluene (127 mL) was heated at reflux for 3 h. The mixture was cooled to rt and the precipitate was collected by filtration, washed with toluene and water, and air dried. The solid was suspended in methanol and the precipitate was collected by filtration, washed with methanol and air dried to provide ethyl 5-bromo-8-carbamoyl-9H-carbazole-2-carboxylate (7.68 g). The filtrate was concentrated and the residue was suspended in methanol. The precipitate was collected by filtration, washed with methanol and air dried to provide additional product (0.60 g) for a total of 8.28 g (90%). 1H NMR (400 MHz, DMSO-d6) δ 12.03 (s, 1H) 8.69 (d, J=8.57 Hz, 1H) 8.51 (d, J=1.10 Hz, 1H) 8.26 (br. s., 1H) 7.93 (d, J=8.13 Hz, 1H) 7.87 (dd, J=8.57, 1.54 Hz, 1H) 7.63 (br. s., 1H) 7.50 (d, J=8.13 Hz, 1H) 4.37 (q, J=7.03 Hz, 2H) 1.37 (t, J=7.14 Hz, 3H). Mass spectrum m/z 361, 363 (M+H)+.

Provenance & Evidence