Cyclohexylidenedehyde (CAS NO.: ), which is known as , cyclohexylidene-, could be produced through the following synthetic routes.

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) and 30 ml. of dry tetrahydrofuran. The system is flushed with nitrogen and a solution of 30.2 g. (0.116 mole) of diethyl 2-(cyclohexylamino)vinylphosphonate 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 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 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. 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%) of cyclohexylideneacetaldehyde, b.p. 78–84° (12 mm.), containing ca. 15% of the isomeric cyclohexenylacetaldehyde.

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