[CH:1]1([OH:13])[CH2:12][CH2:11][CH2:10][CH:9]=[CH:8][CH2:7][CH2:6][CH:5]=[CH:4][CH2:3][CH2:2]1.[CH2:14]([O:16][CH2:17]OCC)[CH3:15].[Br-].[Li+].O.C1(C)C(S(O)(=O)=O)=CC=CC=1>CC(OC)(C)C>[CH2:14]([O:16][CH2:17][O:13][CH:1]1[CH2:12][CH2:11][CH2:10][CH:9]=[CH:8][CH2:7][CH2:6][CH:5]=[CH:4][CH2:3][CH2:2]1)[CH3:15]To a mechanically stirred mixture of 4,8-cyclododecadien-1-ol (5.4 g, 30 mmol; in the form of a 47% E,Z-, 48% Z,E- and 5% E,E isomer mixture), formaldehyde diethyl acetal (31.2 g, 294 mmol) and lithium bromide (0.52 g, 6 mmol) was added toluene sulphonic acid monohydrate (0.57 g, 3 mmol). The mixture was stirred at room temperature for 3 hours, then diluted with MTBE, washed with aqueous NaHCO3, water and brine. The solvent was evaporated and the product purified by liquid chromatography (silica gel 230 g; eluent=heptane/ethyl acetate 95/5).
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