Potassium Carbonate → 2-(1H-Thieno[3,2-c]pyrazol-3-yl)-1H-indole-6-carboxylic acid methyl ester (HRID 2111187)｜HGS AIchem

実験手順

To a solution of 1H-Indole-6-carboxylic acid methyl ester [26.65 g, 146 mmol, Intermediate (33)] and 4-(dimethylamino)pyridine (230 mg) in anhydrous tetrahydrofuran (490 mL) is added di-tert-butyl-dicarbonate (1M in tetrahydrofuran, 150 mL) drop wise over 40 minute periods. Stirred at room temperature for 100 minutes. The solvent is removed in vacuo and the mixture is redissolved in ethyl acetate (400 mL). The ethyl acetate layer is washed with water (20 mL), 0.5 N hydrochloric acid (20 mL), 10% NaHCO3 (20 mL), water (20 mL), brine and dried over sodium sulfate then filtered over 5 g silica gel cartridge. The filtrate is reduced in vacuo to solid. The solid is recrystallized from a mixture of ethyl acetate and heptane to give indole-1,6-dicarboxylic acid 1-tert-butyl ester 6-methyl ester as a white solid (18.53 g). The recrystallisation step is repeated to give a second crop of indole-1,6-dicarboxylic acid 1-tert-butyl ester 6-methyl ester as a white solid (16.3 g). A third crop (5.17 g) of indole-1,6-dicarboxylic acid 1-tert-butyl ester 6-methyl ester is obtained from the mother liquor by silica gel chromatography; total yield of indole-1,6-dicarboxylic acid 1-tert-butyl ester 6-methyl ester [40 g, 100%, Intermediate (34)]; 1H NMR (cdcl3) δ 8.886 (1H, s), 7.937 (1H, d), 7.764 (1H), 7.621 (1H, d), 6.636 (1H), 3.972 (3H, s), 1.734 (9H, s); LC/MS: 276 (M+H). Step 2. A solution of indole-1,6-dicarboxylic acid l-tert-butyl ester 6-methyl ester [13.32 g, 48.38 mmol, Intermediate (34)] and triisopropyl borate (13.65 g, 72.58 mmol) in anhydrous tetrahydrofuran (200 mL) is cooled to 0° C. under nitrogen. To it is added LDA (1.8 M in heptane/tetrahydrofuran/ethylbenzene, 35 mL) drop wise over 40 minute periods. Stirred at 0° C. for 1.5 hours. The reaction is quenched by the addition of 3N hydrochloric acid until pH˜4 on pH paper. After stirring at 0° C. for 5 minutes, the mixture is partitioned between ethyl acetate (200 mL) and water (50 mL). The ethyl acetate layer is washed with brine and dried over sodium sulfate. The residue is purified on 300 g silica gel cartridge (30 to 50% ethyl acetate gradient in heptane then 100% ethyl acetate). The fractions containing higher Rƒ spot are combined and removed solvent in vacuo to give off-white solid (2.32 g). 1HNMR and M/S confirmed it as recovered starting material, indole-1,6-dicarboxylic acid 1-tert-butyl ester 6-methyl ester. The fractions containing lower Rf spot are combined and removed solvent in vacuo. The residual solid (14.2 g) is triturated with acetonitrile and water to give 6-methoxycarbonyl-1-tert-butoxycarbonyl-indole-2-boronic acid [11.8 g, 76.5%, Intermediate (35)] as a beige solid; 1H NMR [(CD3)2SO)]: δ 8.764 (1H, s), 8.311 (2H, s, B(OH)2), 7.795 (1H, d), 7.675 (1H, d), 6.713 (1H, s), 3.876 (3H, s), 1.621 (9H, s). Step 3. A mixture of 6-methoxycarbonyl-1-tert-butoxycarbonyl-indole-2-boronic acid (3.24 g, 10.15 mmol Intermediate (35)], 3-iodo-thieno[3,2-c]pyrazole-1-carboxylic acid tert-butyl ester [2.37 g, 6.77 mmol, Example 5B above], [1,1′-bis(diphenylphosphino)-ferrocene]dichloropalladium with dichloromethane adduct (552 mg, 0.676 mmol), cesium carbonate (6.61 g, 20.29 mmol) and a mixture of 1,4-dioxane/water (40:10 mL). The resulting mixture is heated at 82° C. oil bath for 3 hours under nitrogen. The reaction mixture is poured into ethyl acetate (300 mL). The ethyl acetate layer is washed twice with water (20 mL), brine and dried over sodium sulfate. The crude reaction product is purified on 110 g silica gel cartridge (3% of a mixture of ethyl acetate in methylene chloride and 97% heptane) to afford 2-(1-tert-butoxycarbonyl-1H-thieno[3,2-c]pyrazol-3-yl)-indole-1,6-dicarboxylic acid 1-tert-butyl ester 6-methyl ester [1.68 g, 50%, Intermediate (36)] as white foam; 1H NMR [(CD3)2SO)]: δ 8.975 (1H, s), 8.017 (1H), 7.669 (1H), 7.583 (1H), 7.379 (1H), 7.048 (1H, s), 3.986 (3H, s), 1.736 (9H, s), 1.440 (9H, s); LC/MS: 498 (M+H). A mixture of 1H-thieno[3,2-c]pyrazol-3-yl)-indole-1,6-dicarboxylic acid 1-tert-butyl ester 6-methyl ester or 2-(1-tert-butoxycarbonyl-1H-thieno[3,2-c]pyrazol-3-yl)-indole-1,6-dicarboxylic acid 6-methyl ester, and 2-(1-tert-butoxycarbonyl-1H-thieno[3,2-c]pyrazol-3-yl)-indole-1,6-dicarboxylic acid 1-tert-butyl ester 6-methyl ester material is also isolated (340 mg). 2-(1-Tert-butoxycarbonyl-1H-thieno[3,2-c]pyrazol-3-yl)-indole-1,6-dicarboxylic acid 1-tert-butyl ester 6-methyl ester [Intermediate (36)] is dissolved in methanol/tetrahydrofuran/water (20 mL, 10:5:3) and treated with potassium carbonate (300 mg). The resulting mixture is stirred at room temperature overnight. The reaction mixture is diluted with ethyl acetate (200 mL) and washed with water, brine and dried over sodium sulfate. The crude is purified on 35 g silica gel cartridge (50% ethyl acetate in heptane then ethyl acetate) to afford 2-(1H-thieno[3,2-c]pyrazol-3-yl)-1H-indole-6-carboxylic acid methyl ester [136 mg, Example 43] as a white powder; 1H NMR [(CD3)2SO)]: δ 13.434 (1H, s), 12.044 (1H, s), 8.093 (1H, s), 7.789-7.631 (3H, m), 7.231 (1H, d, J=5.4 Hz), 6.752 (1H, s), 3.855 (3H, s); LC/MS: 298 (M+H).