[H-].[Na+].[CH2:3]([O:5][C:6]([C:8]1[NH:9][C:10]2[C:15]([CH:16]=1)=[CH:14][C:13]([C:17]([O:19][CH2:20][CH3:21])=[O:18])=[CH:12][CH:11]=2)=[O:7])[CH3:4].[CH3:22]I>CN(C=O)C>[CH2:3]([O:5][C:6]([C:8]1[N:9]([CH3:22])[C:10]2[C:15]([CH:16]=1)=[CH:14][C:13]([C:17]([O:19][CH2:20][CH3:21])=[O:18])=[CH:12][CH:11]=2)=[O:7])[CH3:4]Sodium hydride (60%-suspension, 144 mg, 3.6 mmole) was added to a stirred solution of 1H-indole-2,5-dicarboxylic acid diethyl ester 16 (784 mg, 3.0 mmole) in dry DMF (15.0 ml) and kept at ambient temperature for 30 min. To a resulted reaction mixture MeI (280 μl, 4.5 mmol) was added and kept at ambient temperature for 16 hours and evaporated. The residue was suspended in AcOEt (100 ml) and washed with water (2×20 ml), 0.01 M HCl (3×20 ml) and brine (2×100 ml). The organic layer was dried over sodium sulfate and evaporated to give 800 mg (97%) of 1-methyl-indole-2,5-dicarboxylic acid diethyl ester 17 as a yellow oil. 1H-NMR (DMSO-d6): δ 8.45 (m, 1H, H-4, indole); 8.03 (m, 1H, H-6, indole); 7.40 (m, 1H, H-7, indole); 7.38 (s, 1H, H-3, indole); 4.40 (m, 4H, —OCH2CH3); 4.10 (s, 3H, NCH3, indole); 1.42 (m, 4H, —OCH2CH3).
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