Benzoyl isothiocyanate → N-1H-indol-5-yl-Thiourea

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A solution of 5-aminoindole (8 g, 60.6 mmol) in acetone (150 mL) was reacted with benzoylisothiocyanate (9.88 g, 60. mmol) at RT for about 4 h. The resulting solid was filtered and treated with 2 N NaOH in THF (120 mL). The mixture was refluxed for about 6 h and allowed to warm to RT. The solvent was evaporated off under vacuum. The residue was diluted with water (20 mL) and neutralized to pH 7 with 1 N HCl. The resulting solid was filtered and dried under vacuum to afford 5-indolylthiourea (55-2). 5-Indolyl thiourea (0.01 mol) and ethyl bromopyruvate (0.011 mol) were dissolved in 3 mL ethanol and held at reflux for 2 h. The reaction was cooled, the crystalline ethyl 2-(1H-indol-5-ylamino)thiazole-4-carboxylate (55-3) was collected by filtration and washed with ethanol. Refluxing the mixture of ethyl esters with the NaOH-ethanol solution gave 2-(1H-indol-5-ylamino)thiazole-4-carboxylic acid (55-4) which was used directly in next steps. To a mixture of the crude acid (2.5 mmol), EDCI (2.9 mmol), HOBt (2.6 mmol) and NMM (5.3 mmol) in CH2Cl2 (30 mL) was added HNCH3OCH3HCl salt (2.6 mmol) and stirring continued at RT for overnight. The reaction mixture was diluted with CH2Cl2 (20 mL) and sequentially washed with water, satd. NaHCO3, brine and dried over MgSO4. The solvent was removed under reduced pressure to yield a crude product, which was purified by column chromatography to obtain pure compound 2-(1H-indol-5-ylamino)-N-methoxy-N-methylthiazole-4-carboxamide (55-5) (45.6% yield for overall 5 steps). At −78° C., to a solution of 5-bromo-1,2,3-trimethoxybenzene (1.235 g, 5.0 mmol) in 30 mL THF was charged n-BuLi in hexane (2.5 N, 2.4 mL, 6 mmol) under Ar2 protection and stirred for 10 min Weinreb amide (1 mmol) in 10 mL THF was added to lithium reagent and allowed to stir at RT for 2 h. The reaction mixture was quenched with satd. NH4Cl, extracted with ethyl ether, dried with MgSO4. The solvent was removed under reduced pressure to yield a crude product, which was purified by column chromatography to obtain pure compound 55 (51.7% yield). 1H NMR (300 MHz, CDCl3) δ 8.29 (br, 1H), 7.68 (d, 1H), 7.46 (s, 2H), 7.39 (s, 1H), 7.36 (s, 1H), 7.28-7.26 (m, 1H), 7.15-7.12 (m, 1H), 6.55 (m, 1H), 3.93 (s, 3H), 3.89 (s, 6H). MS (ESI) m/z 432.1 (M+Na)+, 408.0 (M−H)−.

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