[Si]([O:8][C:9]1[CH:10]=[C:11]([CH:16]=[CH:17][C:18]=1[O:19][Si](C(C)(C)C)(C)C)[CH:12]=[CH:13][CH2:14][OH:15])(C(C)(C)C)(C)C.Cl>C(Cl)Cl.O=[Mn]=O>[CH:16]1[C:11](/[CH:12]=[CH:13]/[CH:14]=[O:15])=[CH:10][C:9]([OH:8])=[C:18]([OH:19])[CH:17]=13,4-Bis-(t-butyldimethylsilyloxy)cinnamyl alcohol (7.88 g, 20 mmol) was dissolved in 1000 mL CH2Cl2, 17.2 g activated MnO2 (200 mmol) were added and the mixture was vigorously stirred for 24 h at 20° C. MnO2 was filtered off and the filtrate was taken to dryness. To the obtained 3,4-bis(tBDMS)caffeoyl aldehyde 250 mL of CHCl3 was added followed by addition of n-Bu4NF monohydrate (11.6 g, 40 mmol). The mixture was stirred at 20° C. for 30 min and worked up with 300 mL of 5% HCl. Chloroform layer was separated, washed with H2O, dried with Na2SO4 and taken to dryness. The residue was purified on a silica gel column, eluent MeOH—CHCl3, 1:4+1% AcOH. The solvents were evaporated and the crystalline residue was washed with CHCl3 to give caffeoyl aldehyde (1.77 g, 54%). M.p. 200 -202° C., λmax 222, 239, 249, 342 nm. 1H-NMR (δ, ppm): 6.54 (dd, 1H, J 7.7 and 15.8 Hz, Hα), 6.91 (d, 1H, J 8.2 Hz, H5), 7.12 (br.d, 1H, J 8.2 Hz, H6), 7.21 (br.s, 1H, H2), 7.52 (d, 1H, J 15.8 Hz, H), 9.62 (d, 1H, J 7.7 Hz, CHO).
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