反应详情

Step 4 Preparation of 7-Chloro-2-ethyl-5-fluoro-4-nitrobenzoxazole as an Intermediate 7-Chloro-2-ethyl-5-fluorobenzoxazole (0.9 g) was slowly added to a mixture of sulfuric acid (9 ml) and nitric acid (0.6 ml) at −40° C. The dryice-acetone bath was removed and the mixture stirred for 2 hours. Ice-water was added and the mixture was extracted with ether. The organic phase was dried over anhydrous sodium sulfate and concentrated to an oil under reduced pressure. The residue was purified by column chromatography on silica gel using 5% ether in hexane. The desired product was obtained as a white solid [0.35 g, 1H-NMR (CDCl3, 300 MHz): 1.48(3H, t, J=7.6 Hz), 3.07(2H, q, J=7.6 Hz), 7.27(1H, d, J=10.5 Hz) ppm], along with a by-product, 7-chloro-2-ethyl-5-fluoro-6-nitrobenzoxazole (0.49 g).

1. customThe dryice-acetone bath was removed
2. additionIce-water was added
3. extractionthe mixture was extracted with ether
4. dry with materialThe organic phase was dried over anhydrous sodium sulfate
5. concentrationconcentrated to an oil under reduced pressure
6. customThe residue was purified by column chromatography on silica gel using 5% ether in hexane