A mixture of
63.1 g. (0.5 mole) of 2-methyl-1,3-cyclohexanedione (Note
1),
52.6 g. (0.75 mole) of methyl vinyl ketone (Note
2), about
0.25 g. (3 pellets) of potassium hydroxide, and
250 ml. of absolute methanol is placed in a
500-ml. round-bottomed flask fitted with a
reflux condenser and a
drying tube (Note
3). The mixture is heated under reflux for 3 hours, and the dione gradually goes into solution. At the end of this period,
methanol and the excess
methyl vinyl ketone are removed by distillation under reduced pressure (Note
4) and (Note
5). The residual liquid is dissolved in
250 ml. of benzene, a
Dean-Stark phase-separating head is attached, and 20 ml. of solvent is removed by distillation at atmospheric pressure to remove traces of water and
methanol. The solution is cooled well below the boiling point,
3 ml. of pyrrolidine is added (Note
6) and the mixture held at reflux for about 30 minutes, during which time about 9 ml. of water collects in the
trap. Refluxing is continued for an additional 15 minutes after the separation of water ceases. The water collected is removed, and then 50 ml. of solvent is distilled. The reddish reaction mixture is cooled to room temperature and diluted with
150 ml. of ether. This solution is washed with 100 ml. of distilled water containing
15 ml. of 10% hydrochloric acid and 100 ml. of water. The aqueous extracts are extracted with
50 ml. of ether (Note
7), and the combined organic layers are washed with three 100-ml. portions of water, then with saturated salt solution and dried over
magnesium sulfate. The solvents are then removed, and on distillation of the residue (
82–85 g.) (Note
8) at 0.5–1.0 mm. (Note
9) the material, b.p.
117–145°, is collected and diluted with
5 ml. of ether. The distillate is placed overnight in a refrigerator, the resulting crystals are then collected by rapid filtration and washed with about
25 ml. of cold ether (Note
10) and (Note
11). The first crop of diketone weighs
50–53 g. and is colorless. The combined mother liquors are redistilled to obtain a further
4–6 g. of crystalline product. A yield of
56–58 g. (
63–65% based on dione) of
1,6-dioxo-8a-methyl-1,2,3,4,6,7,8,8a-octahydronaphthalene, m.p.
47–50°, suitable for most other purposes, is obtained (Note
12).