Pyridine-3-carboxaldehyde O-methyloxime (I) is prepared either by methylation of 3-pyridinealdoxime sodium salt or by condensation of 3-pyridinecarboxaldehyde with methoxylamine in water. Quaternization of (I) with ethyl iodide gives 3-(methoxyiminomethyl)-1-ethylpyridinium iodide (II), which is reduced by means of sodium borohydride in methanol to 1-ethyl-1,2,5,6-tetrahydropyridine-3-carboxaldehyde O-methyloxime (III). Cleavage of the ethyl group is obtained by reaction with 4-chlorophenylchloroformate in refluxing dichloroethane to yield RU 47213. Ru 47213 is obtained as pure (E)-isomer. Under UV irradiation in toluene it is partially converted into the sterically unfavored (Z)-isomer.