A.
2,2-Dimethyl-4-oxopentanal. (See (Note
1).)
Oxygen is bubbled for 2 hr through a stirred solution of
copper(I) chloride (32.8 g, 0.33 mol),
palladium(II) chloride (1.19 g, 0.007 mol),
829 mL of dimethylformamide, and 331 mL of water in a
2-L, three-necked, round-bottomed flask cooled in a
water bath.
2,2-Dimethyl-4-pentenal (185.6 g, 1.66 mol) (Note
2) is added to the solution and
oxygen is bubbled through for an additional 60 hr at room temperature. The solution is acidified to litmus with
10% hydrochloric acid and extracted 4 times with
200 mL of ethyl ether. The combined organic layers are washed 3 times with
200 mL of saturated sodium chloride solution and dried over
sodium sulfate. The
ether is removed first by rotary evaporation and then under reduced pressure (0.2 mm). In this way
133.6 g (1.04 mol) of keto-aldehyde is obtained in
62.7% yield. The original aqueous layer is saturated with
sodium chloride and extracted 5 times with
200 mL of anhydrous ethyl ether. The combined organic layers are washed 3 times with
200 mL of saturated sodium chloride solution and dried over
sodium sulfate. Solvent is removed by rotary evaporation and
vacuum pump. An additional
31.5 g (0.25 mol) of keto-aldehyde is recovered to give a total yield of
78% (Note
3), bp
32°C (0.3 mm) (Note
4).
B.
4,4-Dimethyl-2-cyclopenten-1-one. A
3-L, round-bottomed flask, containing a solution of
600 mL of aqueous 5% potassium hydroxide,
300 mL of tetrahydrofuran,
1350 mL of ethyl ether, and
165.1 g (1.29 mol) 2,2-dimethyl-4-oxopentanal, is equipped with a
mechanical stirrer and a
reflux condenser. The solution is heated under reflux for 66 hr under a
nitrogen atmosphere. On completion, the organic layer is washed 3 times with
200 mL of saturated sodium chloride solution and dried over
sodium sulfate. The aqueous layer is extracted 3 times with
200 mL of anhydrous ethyl ether. The resulting organic layers are washed 3 times with saturated
sodium chloride solution and dried over
sodium sulfate. All organic layers are evaporated using
aspirator vacuum and a
rotary evaporator and combined. The residual
ether is removed under reduced pressure to yield
89.7 g (
63%) of
4,4-dimethyl-2-cyclopenten-1-one, bp
32°C (0.3 mm) (Note
5),(Note
6),(Note
7).