[Synthesis]
A degassing mixture was prepared from methyl 3-aminobenzoate (10.0 g, 0.061 mol) and copper(II) acetate decahydrate (36.2 g, 0.182 mol) in dimethyl sulfoxide (50 mL). Acetone (100 mL) was added to the reaction flask followed by palladium(II) acetate (0.270 g, 0.001 mol). The reaction mixture was heated at 80 °C for 48 hours. After completion of the reaction, it was cooled to room temperature and the reaction mixture was filtered through a diatomaceous earth pad and the filtrate was diluted with water (80 mL). The aqueous phase was extracted with ethyl acetate (3 x 100 mL), the organic phases were combined and dried over anhydrous sodium sulfate. The organic layer was concentrated under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography using gradient elution with 5-7% ethyl acetate in hexane solution to obtain the target product methyl 2-methyl-1H-indole-6-carboxylate (LVII, 4.8 g, 83% yield) as a light yellow solid. The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3) and mass spectrometry (ESI, positive mode): 1H NMR δ 8.26 (brs, 1H), 8.04 (s, 1H), 7.77 (dd, J = 8.3, 3.4 Hz, 1H), 7.50 (d, J = 8.3 Hz, 1H), 6.26 (s, 1H), 3.92 (s, 3H), 2.47 (s, 3H); MS m/z 190 (MH+). |