Organic Syntheses, CV 5, 539
Submitted by Walter F. Gannon and Herbert O. House
1.
Checked by William E. Parham, Wayland E. Noland, George Meisters, and Allan M. Huffman.
1. Procedure
In a
2-l. flask fitted with a total-reflux, variable-take-off distillation head is placed a solution of
53 g. (0.472 mole) of dihydroresorcinol (Note
1),
2.3 g. of p-toluenesulfonic acid monohydrate and
250 ml. of absolute ethanol in
900 ml. of benzene. The mixture is heated to boiling and the azeotrope composed of
benzene, alcohol, and water is removed at the rate of 100 ml. per hour. When the temperature of the distilling vapor reaches 78° (Note
2), the distillation is stopped and the residual solution is washed with four
100-ml. portions of 10% aqueous sodium hydroxide which have been saturated with
sodium chloride. The resulting organic solution is washed with successive 50-ml. portions of water until the aqueous washings are neutral and then concentrated under reduced pressure. The residual liquid is distilled under reduced pressure. The yield of
3-ethoxy-2-cyclohexenone (Note
3), b.p.
66–68.5°/0.4 mm. or
115–121°/11 mm.,
n29D 1.5015, is
46.6–49.9 g. (
70–75%).
2. Notes
1. The preparation of
dihydroresorcinol was described in an earlier volume of this series.
2
2. This distillation requires 6–8 hours.
3. The product may be analyzed by gas chromatography on an
8 mm. × 215 cm. column heated to 220–240° and packed with Dow-Corning Silicone Fluid No. 550 suspended on 50–80 mesh ground firebrick. The chromatogram obtained with this column exhibits a single major peak. The ultraviolet spectrum of an
ethanol solution of the product has a maxium at 250 mμ (ε = 17,200).
3. Discussion
The 3-alkoxy-2-cyclohexenones are useful intermediates in the synthesis of certain cyclohexenones. The reduction of
3-ethoxy-2-cyclohexenone with
lithium aluminum hydride followed by hydrolysis and dehydration of the reduction product yields
2-cyclohexenone.
10 Similarly, the reaction of 3-alkoxy-2-cyclohexenones with organometallic reagents followed by hydrolysis and dehydration of the addition product affords a variety of 3-substituted 2-cyclohexenones.
3,5,6,8
This preparation is referenced from:
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