反应详情

温度

-7 °C

The synthesis of the precursor 4,4-dimethoxy-3-methylbutan-2-one was performed in analogy to E. E. Royals and K. C. Brannock (J. Am. Chem., 1953, 75, 2050-2053) and yielded a mixture of 58% of the desired precursor, 24% of the byproduct 1,1-dimethoxy-pentan-3-one and about 18% elimination product. 102 g of this mixture (0.405 mol of 4,4-dimethoxy-3-methylbutan-2-one) were dissolved in 30 ml of methanol and added dropwise to 0.698 mol of N-hydroxyurea in 400 ml of 2M HCl, while the internal temperature was maintained at −10 to −4° C. The solution was thawed to room temperature, stirred for 1 h, and then evaporated to dryness. The residue was slurried with 200 ml of acetone, the solid filtered off and washed with little ice-cold acetone. After drying, the crude product was heated with 150 ml of ethanol to boiling, filtered hot, concentrated to 50 ml and cooled to −18° C. The precipitated solid was filtered off, washed with little ethanol and dried. 20 g of this solid was again recrystallized from 100 ml of ethanol, and finally 10 g (12% yield) of the title compound were obtained (content of 85% the title compound and 13% ammonium chloride).

1. customBrannock (J. Am. Chem., 1953, 75, 2050-2053) and yielded
2. customwas thawed to room temperature
3. customevaporated to dryness
4. filtrationthe solid filtered off
5. washwashed with little ice-cold acetone
6. customAfter drying
7. temperaturethe crude product was heated with 150 ml of ethanol
8. filtrationfiltered hot
9. concentrationconcentrated to 50 ml
10. temperaturecooled to −18° C
11. filtrationThe precipitated solid was filtered off
12. washwashed with little ethanol
13. customdried
14. custom20 g of this solid was again recrystallized from 100 ml of ethanol