Research on the synthesis of indole compounds and the improvement of methods are constantly being reported.
According to literature reports, the main methods include the Fischer synthesis, LB synthesis, Reissert method, and the "indole-indoline-indole" method. Among these, the Fischer synthesis is suitable for synthesizing pyrrole-substituted indole derivatives, the LB synthesis is suitable for synthesizing benzene-substituted indole derivatives, the Reissert method is the preferred method for synthesizing 2-substituted indoles, and the "indole-indoline-indole" method can prepare 5-substituted indole compounds simply and mildly. This paper uses indole as a starting material and employs the "indole-indoline-indole" method to synthesize 5-bromo-7-nitroindoline. The synthetic reaction formula for 5-bromo-7-nitroindoline is shown in the figure below: Figure 1. Synthesis formula of 5-bromo-7-nitroindoline. Experimental procedure: 5-bromo-7-nitroindoline, water, and aluminum trichloride were added to a reactor and heated under reflux. Zinc powder was added in batches, and the reaction was monitored by thin-layer chromatography (developing solvent: V(petroleum ether):V(ethyl acetate) = 4.1, Qingdao marine thin-layer chromatography silica gel plate). After 5 hours, the reaction was complete. The mixture was filtered to remove excess zinc powder. The filtrate was adjusted to pH 8 with sodium hydroxide solution. The mixture was extracted three times with diethyl ether. The ether layer was washed successively with water and saturated brine, dried over anhydrous sodium sulfate, filtered, and distilled to obtain pale yellow crystals of 5-bromo-7-nitroindoline.
