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To a 250 mL three-necked flask, 2-bromocarbazole (6.0 g, 24.38 mmol), sodium hydroxide solution (50%) 4 ml, tetrabutylammonium bromide (0.4 g, 1.24 mmol), and the temperature was stirred for 5 min at room temperature. Bromine hexane (8.045 g, 48 mmol) was added dropwise with a syringe.After 12 h of reaction, the eluent was purified by column chromatography to petroleum ether to afford product 1a as an oil, which, after vacuum drying, weighed 7.57 g (yield about 94%).