Methanesulfonic Acid → 5-Chloro-2-(2-fluoronitrobenzen-5-yl)benzoxazole

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Reaction Steps

4-Fluoro-3-nitrobenzoic acid (25.0 g, 135 mmol), 2-amino-4-chlorophenol (21.3 g, 149 mmol), CHCl3 (500 mL), and WSC (28.5 g, 149 mmol) were added together and stirred at room temperature for 2 hours. The reaction mass was concentrated, and then the residue was washed with water and ethanol. To a dioxane (500 mL) solution of the solid obtained was added methanesulfonic acid (81.9 g, 811 mmol), and this was heated to reflux for 18 hours. After the reaction solution was cooled, water was added, and the precipitated crystals were filtered, and after being washed with water were dried to yield the title compound (31.0 g, 78% yield) as reddish-brown crystals.

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