Phosphorus pentachloride → 2-(dimethylamino)-4-(trifluoromethyl)-6H-1,3-oxazin-6-one

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A solution of ethyl 3-[N-(N,N-dimethylcarbamoyl)-amino]-4,4,4-trifluorocrotonate (5.08 g, 0.02 mol) in phosphorus oxytrichloride (3 mL) is treated with phosphorus pentachloride (4.16 g, 0.02 mol) in three portions at 15 minute intervals, stirred for 30 minutes, and quenched with ice and water. The resultant aqueous mixture is extracted with ethyl acetate. The organic layer is washed sequentially with saturated sodium bicarbonate and water, and evaporated to give the title product as a white solid (3.9 g, 93.8% yield) which is identical by 1H and 19F NMR to a sample prepared by the literature procedure (Bull. Soc. Chem. Belg. 101, 313, 1992). The title product is further purified by crystallization from heptane (74.5% crystallized yield).

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