[OH:1][CH2:2][CH:3]=[C:4]([CH3:15])[CH:5]=[CH:6][CH:7]=[C:8]([CH3:14])[C:9]([O:11][CH2:12][CH3:13])=[O:10]>C(Cl)Cl.[O-2].[O-2].[O-2].[Ni+3].[Ni+3]>[CH3:14][C:8](=[CH:7][CH:6]=[CH:5][C:4]([CH3:15])=[CH:3][CH:2]=[O:1])[C:9]([O:11][CH2:12][CH3:13])=[O:10]21 g of ethyl 8-hydroxy-2,6-dimethyl-octa-2,4,6-trien-1-oate in 500 ml of methylene chloride are stirred at -25° C. for 2 hours with 50 g of nickel peroxide (prepared in Example 1 and containing 6.1% of active oxygen). The mixture is then filtered, the solution evaporated to 100 ml, treated with 250 ml of n-hexane and again evaporated to 100 ml. The residual solution is cooled to 50° C., seeded with crystals of ethyl 2,6-dimethyl-8-oxo-octa-2,4,6-trien-1 -oate and left to crystallise for 30 minutes at 0° C. After filtration under suction and drying of the crystals, there are obtained 16.5 g (79.5%) of pure ethyl 2,6-dimethyl-8-oxo-octa-2,4,6-trien-1-oate.
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