O=O.[OH:3][CH2:4][CH:5]=[C:6]([CH3:17])[CH:7]=[CH:8][CH:9]=[C:10]([CH3:16])[C:11]([O:13][CH2:14][CH3:15])=[O:12].CC1(C)CCCC(C)(C)[NH+]1[O-].[Cl-].[Na+]>CN(C)C=O.[Cu]Cl>[CH3:16][C:10](=[CH:9][CH:8]=[CH:7][C:6]([CH3:17])=[CH:5][CH:4]=[O:3])[C:11]([O:13][CH2:14][CH3:15])=[O:12]From 50 to 60 ml of oxygen per minute were passed through a solution of 30.0 g (142.7 millimoles) of ethyl 8-hydroxy-2,6-dimethylocta-2,4,6-trien-1-oate (isomer mixture) and 2.23 g (14.3 millimoles) of 2,2,6,6-tetramethylpiperidine 1-oxide in 75 ml of N,N-dimethylformamide, after the addition of 1.42 g (14.3 millimoles) of copper(I) chloride, the temperature being kept at from 20° to 35° C. with the aid of an ice bath. After 1 hour, the mixture was poured onto 150 ml of aqueous sodium chloride solution and extracted with methyl tert-butyl ether. The organic phase was first washed with a solution of sodium iodide in 5% strength hydrochloric acid, shaken with aqueous sodium thiosulfate solution, washed with water and then dried over sodium sulfate, after which the solvent was removed under reduced pressure. 27.3 g (92% yield) of ethyl 2,6-dimethyl-8-oxoocta-2,4,6-trien-1-oate were obtained.
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