Cesium carbonate → 4-Chloro-2-{4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzenesulfonyl-(t-butoxycarbonyl)amino}-benzoic acid methyl ester

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A mixture of the title E compound, 2-[(4-hydroxybenzenesulfonyl)-(t-butoxycarbonyl)-amino]-4-chloro-benzoic acid methyl ester (300 mg, 0.73 mmol), the title F compound, methanesulfonic acid 2-(5-methyl-2-phenyl-oxazol-4-yl)-ethyl ester (246 mg, 0.87 mmol) and cesium carbonate (475 mg, 1.46 mmol) is stirred in DMF at 60° C. overnight. The mixture is cooled and the product is taken up in EtOAc. The solution is washed with brine, dried over anhydrous magnesium sulfate, and concentrated to give the crude product which is purified by flash chromatography on silica gel using an EtOAc (15%)-hexane (85%) mixture as the eluent to afford 4-chloro-2-{4-[2-(5-methyl-2-phenyl-oxazol-4-yl)-ethoxy]-benzenesulfonyl-(t-butoxycarbonyl)amino}benzoic acid methyl ester as a white foam.

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