A
1-l., three-necked, round-bottomed flask, fitted with a
magnetic stirrer,
dropping funnel, and
nitrogen inlet is charged with
5.45 g. (0.116 mole) of sodium hydride (51% oil dispersion) (Note
1) and
30 ml. of dry tetrahydrofuran (Note
2). The system is flushed with
nitrogen and a solution of
30.2 g. (0.116 mole) of diethyl 2-(cyclohexylamino)vinylphosphonate [
Org. Synth., Coll. Vol. 6, 448 (1988)] in
90 ml. of dry tetrahydrofuran is added dropwise to the stirred mixture over a period of 15 minutes. During the addition the temperature is maintained at 0–5° with an
ice bath. The mixture is stirred for an additional 15 minutes at 0–5° to ensure complete reaction. A solution of
10.3 g. (0.105 moles) of cyclohexanone (Note
3) in
70 ml. of dry tetrahydrofuran is added dropwise to the mixture over a period of 20 minutes, so that the temperature does not exceed 5°. The mixture is stirred for an additional 90 minutes at 20–25° in a
water bath. During the stirring a gummy precipitate of
sodium diethyl phosphate is observed. The mixture is poured into 500 ml. of cold water and extracted with three
300-ml. portions of diethyl ether. The combined ether extracts are washed twice with 200 ml. of saturated aqueous salt solution, dried over anhydrous
sodium sulfate, and distilled under reduced pressure (35 mm.) at 25–30°. The residue is dissolved in
300 ml. of benzene and transferred to a
3-l., three-necked, round-bottomed flask equipped with a stirrer and a
reflux condenser. To this solution is added a solution of
72 g. (0.57 mole) of oxalic acid dihydrate in 900 ml. of water (Note
4). The stirred mixture is refluxed for 2 hours under
nitrogen, cooled, and transferred to a
separatory funnel. The aqueous layer is extracted with two
300-ml. portions of ether. The combined organic extracts are washed with 200 ml. of water, then with 200 ml. of saturated aqueous salt solution, and dried over anhydrous
sodium sulfate, and distilled under reduced pressure (35 mm.) at 25–30°. The residue is transferred to a
30-ml., round-bottomed flask and distilled under reduced pressure through a
5-cm. Vigreux column, yielding
10.8 g. (
83%, (Note
5)) of
cyclohexylideneacetaldehyde, b.p.
78–84° (12 mm.), containing
ca. 15% of the isomeric
cyclohexenylacetaldehyde (Note
6).