| 94% |
With sodium hydroxide In tetrahydrofuran; methanol; water at 20℃; for 18 h; |
To a solution of ethyl 1,3-benzothiazole-5-carboxylate (5.30 g, 25.6 mmol) in a mixture of methanol (150 mL), tetrahydrofuran (40 mL) and water (5 mL) was added a 50percent aqueous solution of sodium hydroxide (10 mL). The mixture was maintained at rt for 18 h and was concentrated. The residue was partitioned between water (300 mL) and diethyl ether (200 mL) and the organic layer was removed. Concentrated hydrochloric acid was added to the aqueous layer to adjust the pH to 4 and the mixture was extracted with ethyl acetate (3 x 300 mL). The combined extracts were washed with brine (200 mL), dried over anhydrous sodium sulfate, and concentrated to yield 4.30 g (94percent) the acid. |
| 94% |
Stage #1: With sodium hydroxide; water In tetrahydrofuran; methanol at 20℃; for 18 h;
Stage #2: With hydrogenchloride In water |
To a solution of 4-chloro-3-nitrobenzoic acid (99.2 mmol) in N, N-dimethylformamide (400 mL) was added potassium carbonate (254 mmol). After 30 min, ethyl iodide (119 mmol) was added and the reaction mixture was heated at 50 °C for 4 h. Water (3 L) was added and the mixture was extracted with diethyl ether (2 x 500 mL). The organic extracts were combined, washed with brine (1 L), dried over anhydrous sodium sulfate and concentrated. The residue was crystallized from hexanes, thus providing the ester in 86percent yield.'H NMR (500 MHz, CDC13) 8 8. 51 (d, 1H), 8.17 (dd, 1H), 7.65 (d, 1H), 4.43 (q, 2H), 1.42 (t, 3H). Sulfur (49.91 mmol) was dissolved in a solution of sodium sulfide nonahydrate (49.96 mmol) in water (60 mL). This solution was combined with a solution of ethyl 4-chloro- 3-nitrobenzoate (85.36 mmol) in ethanol (100 mL) and the resulting mixture was heated at reflux for 3 h. The hot reaction mixture was poured into water (600 mL) and maintained for 15 min. The product was isolated by filtration and recrystallized from ethanol, thus providing the disulfide in 77percent yield. 1H NMR (500 MHz, CDC13) 8 8.96 (d, 1H), 8.19 (dd, 1H), 7.88 (d, 1H), 4.43 (q, 2H), 1.41 (t, 3H). A mixture of diethyl 4,4'-dithiobis (3-nitrobenzoate) (24.8 mmol) and zinc granules (234 mmol) in formic acid (600 mL) was heated to reflux for 48 h. The mixture was allowed to cool to room temperature and concentrated to dryness. The residue was partitioned between ethyl acetate (500 mL) and saturated aqueous sodium bicarbonate (500 mL). The organic layer was separated, dried over anhydrous sodium sulfate and concentrated. The residue was chromatographed on neutral Alumina (1/1 to 0/1 hexanes/dichloromethane), thus providing the thiazole in 51percent yields NMR (500 MHz, CDCl3) 5 9. 08 (s, 1H), 8.83 (d, 1H), 8.14 (dd, 1H), 8.02 (d, 1H), 4.45 (q, 2H), 1.44 (t, 3H); MS (EI) nilz 208 (M++1). To a solution of ethyl 1, 3-benzothiazole-5-carboxylate (25.6 mmol) in a mixture of methanol (150 mL), tetrahydrofuran (40 mL) and water (5 mL) was added a 50percent aqueous solution of sodium hydroxide (10 mL). The mixture was maintained at rt for 18 h and was concentrated. The residue was partitioned between water (300 mL) and diethyl ether (200 mL) and the organic layer was removed. Concentrated hydrochloric acid was added to the aqueous layer to adjust the pH to 4 and the mixture was extracted with ethyl acetate (3 x 300 mL). The combined extracts were washed with brine (200 mL), dried over anhydrous sodium sulfate, and concentrated thus providing the acid in 94percent yield. |
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