[CH3:1][Si:2]([CH2:5][O:6][C:7]1[CH:14]=[CH:13][C:10]([CH:11]=O)=[CH:9][CH:8]=1)([CH3:4])[CH3:3].C(=[C:18]([C:22]([O-:24])=[O:23])[C:19]([O-:21])=[O:20])(C)C.N1CC[CH2:28][CH2:27][CH2:26]1.C(O)(=O)C>C1(C)C=CC=CC=1.O>[CH3:26][C:27]1([CH3:28])[O:21][C:19](=[O:20])[C:18](=[CH:11][C:10]2[CH:13]=[CH:14][C:7]([O:6][CH2:5][Si:2]([CH3:4])([CH3:3])[CH3:1])=[CH:8][CH:9]=2)[C:22](=[O:23])[O:24]14-(Trimethylsilanylmethoxy)benzaldehyde (obtained in step 1 of Example 1) (5 g, 0.024 mol) and isopropylidenemalonate (3.8 g, 0.0264 mol) in 10 ml of dry toluene in the presence of 0.24 ml of piperidine and 0.14 g of acetic acid are refluxed for 5 hours in a reactor equipped with Dean-Stark apparatus. The water formed is removed azeotropically. The mixture is cooled and the toluene is removed by distillation. The reaction mixture is taken up in 50 ml of diisopropyl ether. The organic phase is washed 3 times with water, dried over sodium sulfate and filtered, and the solvent is evaporated off under vacuum. The yellow oil obtained (7.48 g) is purified by chromatography on a column of silica (eluent: 95/5 heptane/EtOAc). 3.64 g of clean fractions (yield; 45% of the derivative of Example 6 are recovered in the form of a yellow solid:
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