[OH:1][C:2]1[CH:9]=[CH:8][C:5]([CH:6]=[O:7])=[CH:4][CH:3]=1.C(=O)([O-])[O-].[K+].[K+].Br[C:17]([CH3:26])([CH3:25])[C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19].O>CN(C)C=O>[CH:6]([C:5]1[CH:8]=[CH:9][C:2]([O:1][C:17]([CH3:26])([CH3:25])[C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19])=[CH:3][CH:4]=1)=[O:7]24.42 g (200 mmol) of 4-hydroxybenzaldehyde are dissolved in 250 ml of N,N-dimethylformamide and treated with 27.64 g (200 mmol) of potassium carbonate. At 100° C., 53.55 g (240 mmol) of tert-butyl α-bromoisobutyrate are added dropwise. The mixture is stirred for another hour, a further 200 mmol of potassium carbonate and 240 mmol of tert-butyl α-bromoisobutyrate are added and, after 4 hours at 100° C., 1 l of water is added. Following extraction with diethyl ether, washing with 1 N aqeuous sodium hydroxide solution and saturated sodium chloride solution and drying over magnesium sulphate, the solvent is distilled off and the residue is purified by flash chromatography on silica gel (cyclohexane→cyclohexane/ethyl acetate 20:1→10:1→5:1) and dried under reduced pressure. The target compound is obtained in the form of colourless crystals in a yield of 42%.
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