[C:1]([O-:4])(=[O:3])[CH3:2].[Li+].[C:6]1(=O)[CH:11]=[CH:10][C:9](=[O:12])[CH:8]=[CH:7]1.C1CCC=CC=1.[C:20](O)(=[O:22])[CH3:21]>CCCCC.C([O-])(=O)C.[Pd+2].C([O-])(=O)C.[O-2].[O-2].[Mn+4]>[C:1]([O:4][CH:6]1[CH2:7][CH2:8][CH:9]([O:12][C:20](=[O:22])[CH3:21])[CH:10]=[CH:11]1)(=[O:3])[CH3:2]Lit., J. Org. Chem., 49:4619 (1984). To a stirred solution of 2.8 g (12.5 mmol) palladium acetate, 27.2 g (267 mmol) lithium acetate, and 7.64 g (70.7 mmol) benzoquinone in 200 ml acetic acid at room temperature were added 26.1 g (300 mmol) manganese dioxide and a solution of 23.8 ml (250 mmol) 1,3-cyclohexadiene in 400 ml pentane, and stirring continued for 16 h. The two-phase reaction mixture was separated and the acetic acid phase extracted twice with pentane. The combined organic extracts were washed successively with saturated brine, water, and 2 M sodium hydroxide solution, then the organic phases were dried over sodium sulphate and concentrated in vacuo. Recrystallisation from pentane afforded 16.1 g (33%) of the title compound as an off-white crystalline solid. MS m/e (%): 138 ([M−AcOH]+, 8), 96 ([M−AcOH—COCH2]+, 100), 43 (40).
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