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With sodium hydroxide; In ethanol; water; for 4h;Reflux;
General procedure: The appropriate ethyl ester (1c, 3c) (5.8 mmol) was refluxed for4 h in a mixture of equal volumes of aqueous 10% NaOH (20 mL) andEthanol (20 mL). After completion of the reaction, ethanol wasevaporated under reduced pressure and the remaining solutionwasthen extracted with ethyl acetate. The organic layer was discardedwhile the aqueous layer was acidified to pH 3 with aqueous 10%hydrochloric acid. The mixturewas then evaporated under reducedpressure and the solid obtained was then dissolved in methanolwhile the remaining insoluble NaCl was discarded. Evaporating themethanol afforded the desired pure acids 1d and 3d.
With potassium hydroxide; In methanol; water;
After 9.7 g of potassium hydroxide were added to 50 ml of methanol and 50 ml of water, 10.2 g of ethyl 2,4-dimethyl-5-thiazolecarboxylate were added dropwise thereto at room temperature. The reaction was conducted at room temperature for 1 hour, and the reaction mixture was then acidified with 2-N hydrochloric acid. After methanol was distilled off, the crystals were collected through filtration, washed with water, and dried to obtain 6.6 g of the Compound No. 2.1 of the present invention. melting point: from 220 to 225 C.
To a flask containing <strong>[53137-27-2]2,4-dimethylthiazole-5-carboxylic acid</strong> (2.50 g, 15.9 mmol) was added DCM (75 mL) and DMF (3 mL) to afford a homogeneous solution. Then, carbonyldiimidazole (2.84 g, 17.5 mmol) was added and the mixture was stirred at room temperature for 2 hours. N,O-dimethylhydroxylamine hydrochloride (1.90 g, 19.9 mmol) was then added and the reaction mixture was stirred at room temperature for 18 hours, then diluted with water and 1 N NaOH and extracted with DCM (4×50 mL). The combined organics were washed with brine, dried over Na2SO4, filtered and concentrated. Flash chromatography on silica gel (10-40% EtOAc-DCM) provided the title compound as a colorless oil.
To a flask containing <strong>[53137-27-2]2,4-dimethylthiazole-5-carboxylic acid</strong> (2.5 g, 15.9 mmol) was added DCM (75 mL) to give a suspension. DMF (3 mL) was added which resulted in a homogeneous solution. Then, carbonyldiimidazole (2.84 g, 17.5 mmol) was introduced and the mixture was stirred at room temperature for 2 hours. N,O-dimethylhydroxylamine HCl (1.9 g, 19.9 mmol) was then added and the mixture was stirred at room temperature for 18 hours, at which time the reaction mixture was diluted with water and 1 N aqueous NaOH and the aqueous portion was extracted with DCM (4*50 mL). The combined organics were washed with brine, dried over Na2SO4, filtered and concentrated. Chromatography on silica gel (10% EtOAc-DCM increasing to 40% EtOAc) provided the title compound as a colorless oil.
intermediate 17: step aN-methoxy-N,2,4-trimethylthiazole-5-carboxamideTo a flask containing 2,4-dimethylthiazole~5~carboxylic acid (2.5 g, 15.9 mmol) was added DCM (75 mL) to give a suspension . DMF (3 mL) was added which resulted in a homogeneous solution. Then, carbonyldiimidazole (2.84 g, 17.5 mmol) was introduced and the mixture was stirred at, room temperature for 2 hours. N,0-dim.ethymydroxylamine HQ (1 .9 g, 19.9 mmol) was then added and the mixture was stirred at room temperature for 18 hours, at which time the reaction mixture was diluted with water and 5 N aqueous NaOH and the aqueous portion was extracted with DCM (4 x 50 mL). The combined organics were washed with brine, dried over a2S04, filtered and concentrated. Chromatography on silica gel (1 0% EtOAc-DCM increasing to 40% EtOAc) provided the title compound as a colorless oil.
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