[CH3:1][C@@H:2]([CH2:6][CH2:7][CH:8]=[C:9]([CH3:11])[CH3:10])[CH2:3][CH:4]=[O:5].C=O.N1CCC[CH2:15]1.C(O)(=O)CC>C(O)(C)C>[CH3:1][C@@H:2]([CH2:6][CH2:7][CH:8]=[C:9]([CH3:10])[CH3:11])[C:3](=[CH2:15])[CH:4]=[O:5]To a solution of (S)-3,7-dimethyloct-6-enal (3.0 g, 19.45 mmol) in isopropyl alcohol (20 mL) at room temperature. was added 37% aqueous formaldehyde (14.46 mL, 194.5 mmol), pyrrolidine (1.61 mL, 19.45 mmol) and propionic acid (1.45 mL, 19.45 mmol). The mixture was warmed to 45° C. and stirred for 2 hours. The reaction was then cooled to 0° C. and quenched with saturated aqueous sodium bicarbonate (100 mL). The mixture was extracted with dichloromethane and the combined organic phase was washed with brine, dried over anhydrous sodium sulfate and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent:petroleum ether/ethyl acetate=160:1->110:1) to afford the title compound as a colorless oil (3.2 g, Yield: 98%). Rf=0.7 (10:1) petroleum ether/:ethyl acetate); 1H NMR (400 MHz, CDCl3) δ 9.53 (s, 1H), 6.22 (s, 1H), 5.98 (s, 1H), 5.09-5.05 (m, 1H), 2.73-2.67 (m, 1H), 1.94-1.90 (m, 2H), 1.67 (s, 3H), 1.57 (s, 3H), 1.54-1.48 (m, 1H), 1.42-1.37 (m, 1H), 1.06 (d, J=6.8 Hz, 3H) ppm.
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