Hafnium chloride (39.2 mg, 0.122 mmol) was suspended in anisole (3, 0.02 mL) under an argon atmosphere, and then an anisole solution (0.22 mL) of 4-(pivaloyloxy)benzaldehyde (1, 25 mg, 0.121 mmol) and trimethyl cinnamylsilane (2, 46.7 mg, 0.245 mmol) was slowly added dropwise thereto under cooling by ice. The reaction mixture was stirred overnight at room temperature, then a saturated aqueous sodium bicarbonate solution (5 mL) was poured thereto, and the mixture was intensively stirred and extracted by adding diethyl ether (10 mL). The reaction mixture was further extracted two times using diethyl ether (10 mL), and then an organic layer was collected and rinsed with a saturated aqueous sodium chloride solution (5 mL), followed by drying with anhydrous magnesium sulfate and concentration thereof. The residue was purified by thin layer chromatography (hexane/methylene chloride/diethyl ether=4/1/1) to obtain the title compound as a colorless oily substance (37.7 mg, yield 75%, cin/anti mixture).
