[OH:1][C:2]1[CH:9]=[CH:8][C:5]([CH:6]=[O:7])=[CH:4][CH:3]=1.C(=O)([O-])[O-].[Cs+].[Cs+].Br[C:17]([CH3:26])([CH3:25])[C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19]>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]A solution of 24.4 g (200 mmol) of 4-hydroxybenzaldehyde in 100 ml of dimethylformamide is treated with 97.75 g (300 mmol) of caesium carbonate and stirred at 90° C. for 1 h. A solution of 66.93 g (300 mmol) of tert-butyl 2-bromisobutyrate in 100 ml of dimethylformamide is then added dropwise, and the mixture is stirred at 90° C. overnight. The dimethylformamide is distilled off under reduced pressure and the residue is then taken up in ethyl acetate, washed 2× with water, 2× with 1 N aqueous sodium hydroxide solution and 1× with sat. NaCl solution, dried over sodium sulphate and freed from the solvent under reduced pressure. This gives 16.6 g (31%) of tert-butyl 2-(4-formylphenoxy)-2-methylpropionate.
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