[CH3:1][O:2][C:3](=[O:17])[CH2:4][CH2:5][C:6]1[CH:11]=[CH:10][C:9]([OH:12])=[C:8]([C:13]([CH3:16])([CH3:15])[CH3:14])[CH:7]=1.[C:18](O)(=[O:21])[CH:19]=[O:20].C1(C)C=CC(S(O)(=O)=O)=CC=1>O.C(Cl)CCl>[C:13]([C:8]1[C:9]2[O:12][C:19](=[O:20])[CH:18]([OH:21])[C:10]=2[CH:11]=[C:6]([CH2:5][CH2:4][C:3]([O:2][CH3:1])=[O:17])[CH:7]=1)([CH3:14])([CH3:16])[CH3:15]3-(4-hydroxy-3-tert.butylphenyl) propionic acid methyl ester (10.0 g), glyoxylic acid (7.4 g of the 50% solution in water) and p-toluene sulphonic acid (40 mg) are heated in 40 ml ethylene chloride under nitrogen at reflux for 3 hours distilling off all water present and formed during the reaction. The reaction mixtures is washed with water, dried over magnesium sulphate and evaporated under reduced pressure to give 13.0 g of 7-tert.butyl-5-(2-methoxycarbonylethyl)-3-hydroxy-3H-benzofuran-2-one.
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