[CH2:1]([C:3]1([CH3:14])N=[C:7]([CH2:9][CH3:10])[CH2:6][C:5]([CH2:12][CH3:13])([CH3:11])[NH:4]1)[CH3:2].[Br-].[NH4+].Cl.C(=O)([O-])[O-:19].[K+].[K+]>CO>[CH2:1]([C:3]1([CH3:14])[CH:9]([CH3:10])[C:7](=[O:19])[CH2:6][C:5]([CH2:12][CH3:13])([CH3:11])[NH:4]1)[CH3:2]19.6 g of 2,4,6-triethyl-2,6-dimethyl-1,2,5,6-tetrahydropyrimidine and 0.4 g of ammonium bromide were added to 200 ml of methanol. To the mixture was added dropwise 10 g of 37% hydrochloric acid at 10° C., with stirring. After completion of the addition the whole was stirred at room temperature for 4 hours and there was then added a further 20 ml of 18% hydrochloric acid. The mixture was then heated at 30°-40° C. for 7 hours and allowed to stand over night at room temperature. The mixture was made alkaline with 40% aqueous potassium carbonate solution and, after methanol has been distilled off under reduced pressure, the residue was extracted with ether. The ether solution was dried over potassium carbonate and the ether was removed. The residue was subjected to distillation under reduced pressure to yield 2,6-diethyl-2,3,6-trimethyl-4-oxopiperidine as an oil boiling at 91°-93° C./2 mm Hg.
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