反应详情

温度

67.5 °C

1.00 mL (5.84 mmoles) of citral (purchased from Aldrich Chemical Co., Milwaukee, Wis.), 20 mL of acetone (HPLC-grade, purchased from Aldrich Chemical Co.), and 1.66 g of alumina (weakly acidic, activated, Brockmann I, 150 mesh, Aldrich catalog #26,774-0) were added to a 200 mL glass pressure bottle containing a Teflon-coated spin bar. After sweeping the bottle briefly with a stream of nitrogen gas, the bottle was closed; and the mixture was subsequently heated at 65-70° C. (external oil bath temperature) for 20 hours. After cooling the mixture to room temperature, the product was isolated by dilution of the reaction mixture with 160 mL of 3:1 (v/v) ether: dichloromethane and removal of the alumina by filtration through a small pad of Hyflo Super-Cel® filtering aid. For large-scale reactions, fractional distillation of this filtrate would be the only requirement to complete the process of isolating the product. For convenience in a small-scale reaction, the filtrate was washed three times with 140 mL portions of 5% (w/v) aqueous sodium chloride to remove 4-hydroxy-4-methyl-2-pentanone (formed in minor amounts by the self-aldol condensation of acetone), then dried over anhydrous magnesium sulfate, and filtered. Removal of the ether and dichloromethane by evaporation at reduced pressure and subsequent evaporative ("Kugelrohr oven") distillation afforded 1.03 g (91% yield) of the named unsaturated ketone: boiling point 102-110° C. (bath temperature, 0.40 mm). The identity and purity of this compound was ascertained by IR and proton NMR analysis (recorded at 400 MHz). The latter spectrum exhibited a multiplet at δ 7.42 (C-4 vinyl H), a doublet (J=14.8 Hz) at δ 6.08 (C-3 vinyl H), a doublet (J=12 Hz) at δ 6.004 (C-5 vinyl H), a multiplet at δ 5.09 (C-9 vinyl H), a singlet at δ 2.27 (CH3C=O), and signals for three vinyl methyl groups at δ 1.90 (CH3 bonded to C-6), 1.676, and 1.606.

1. additioncontaining a Teflon-coated spin bar
2. customthe bottle was closed
3. temperatureAfter cooling the mixture to room temperature
4. customdichloromethane and removal of the alumina
5. filtrationby filtration through a small pad of Hyflo Super-Cel®
6. filtrationfiltering aid
7. distillationFor large-scale reactions, fractional distillation of this filtrate
8. customof isolating the product
9. customFor convenience in a small-scale reaction
10. washthe filtrate was washed three times with 140 mL portions of 5% (w/v) aqueous sodium chloride
11. customto remove 4-hydroxy-4-methyl-2-pentanone (
12. customformed in minor amounts by the self-aldol condensation of acetone),
13. dry with materialthen dried over anhydrous magnesium sulfate
14. filtrationfiltered
15. customRemoval of the ether and dichloromethane
16. customby evaporation
17. distillationat reduced pressure and subsequent evaporative ("Kugelrohr oven") distillation