反应详情

A mixture of 18a and 18b (2.53 g, 15.9 mmol) was diluted in POCl3 (˜35 mL), and the mixture was heated at reflux for 70 min, before the clear orange solution was cooled to room temperature and poured into ice-H2O (300 mL) in a large beaker. The beaker was immersed in ice and cooled to 0° C. with stirring, and solid NaOH was added until the pH of the mixture was approximately 7. The resultant cloudy suspension was extracted with EtOAc (300 mL) and the organic layers were washed with H2O (100 mL) and sat. aq. NaCl (100 mL). The organic layer was dried over anhydrous sodium sulfate, concentrated, and the residue was purified by flash column chromatography (SiO2), eluting with a gradient of hexanes to 12% ethyl acetate in hexanes to afford orange crystals. Fractional crystallization from hot isopropanol yielded pure 19a (0.850 g, 30%) as light orange iridescent crystals; the analytical data for this compound is identical to prior literature reports. H-NMR (500 MHz; CDCl3): δ 8.05 (d, J=8.5 Hz, 1 H), 8.00 (m, 1 H), 7.71 (d, J=8.3 Hz, 1 H), 7.39 (dd, J=8.3, 1.5 Hz, 1 H), 7.32 (d, J=8.5 Hz, 1 H), 2.56 (s, 3 H).

1. temperaturethe mixture was heated
2. temperatureat reflux for 70 min, before the clear orange solution
3. temperaturecooled to 0° C.
4. extractionThe resultant cloudy suspension was extracted with EtOAc (300 mL)
5. washthe organic layers were washed with H2O (100 mL) and sat. aq. NaCl (100 mL)
6. dry with materialThe organic layer was dried over anhydrous sodium sulfate
7. concentrationconcentrated
8. customthe residue was purified by flash column chromatography (SiO2)
9. washeluting with a gradient of hexanes to 12% ethyl acetate in hexanes
10. customto afford orange crystals
11. customFractional crystallization from hot isopropanol yielded pure 19a (0.850 g, 30%) as light orange iridescent crystals