10075-52-2

124-38-9

400071-95-6

In a 50 mL autoclave fitted with a glass inner tube and a magnetic stir bar, 5-bromo-1-methyl-1H-indole (1a, density 1.05 g/mL; 125 μL, 1.00 mmol), dimethylaluminum chloride (1.0 M hexane solution; 1.0 mL, 1.0 mmol), and toluene (1.0 mL) were added, and the mixture was purged with nitrogen under protection by repeated pressurization and subsequent swelling The final pressure was adjusted to 3.0 MPa using a carbon dioxide purge device.The mixture was stirred at 80 °C for 3 h before the reactor was allowed to cool to room temperature and slowly depressurized. The reaction mixture was quenched with 2 M hydrochloric acid solution and the aqueous layer was extracted with ethyl acetate. The combined organic layers were extracted with 0.5 M sodium carbonate solution and the extract was acidified by adding concentrated hydrochloric acid to release the free carboxylic acid and again extracted with ethyl acetate. The extract was dried with anhydrous magnesium sulfate and evaporated under reduced pressure to obtain the residue, which was purified by column chromatography using chloroform-ethyl acetate (1:1, v/v) as eluent to give 1-methyl-5-bromo-3-indolecarboxylic acid (2a) as crystals (168 mg, 96% yield). The carboxylation reaction of other indole derivatives was carried out in a similar way. The crude product was routinely purified by column chromatography using chloroform-ethyl acetate (1:1, v/v) or pure chloroform-ethyl acetate (1:1, v/v) containing 1% (v/v) acetic acid as eluent. The reaction conditions and product yields are shown in Tables 1 and 2.