[Cr](Cl)([O-])(=O)=O.[NH+]1C=CC=CC=1.[CH3:12]/[C:13](=[CH:18]\[C:19]1[CH:24]=[CH:23][C:22]([CH3:25])=[CH:21][CH:20]=1)/[CH2:14][CH2:15][CH2:16][OH:17].C(OCC)C>ClCCl>[CH3:12]/[C:13](=[CH:18]\[C:19]1[CH:24]=[CH:23][C:22]([CH3:25])=[CH:21][CH:20]=1)/[CH2:14][CH2:15][CH:16]=[O:17]Solid pyridinium chlorochromate (13.2 g, 0.06 mol) was added in one portion to a pre-cooled (−10° C.) solution of (4E)-4-Methyl-5-(4-methylphenyl)-4-penten-1-ol (9.88 g, 0.052 mol) in dry dichloromethane (250 ml) under nitrogen. After 30 minutes, the reaction was warmed up to room temperature. After 1 hour, diethyl ether (700 ml) was added to the reaction. After stirring for 10 minutes, the reaction was filtered through silica gel, rinsing with diethyl ether. The solvent was removed under vacuum and the residue was purified by column chromatography on silica gel (eluent: heptanes/ethyl acetate 10:1) followed by bulb-to-bulb distillation (100° C./0.001 mbar). 3.55 g (yield=36%) of the desired product were obtained.
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