Under an argon atmosphere, hafnium chloride (39.2 mg, 0.122 mmol) is suspended in anisole (3, 0.02 mL), and under ice cooling, an anisole (0.22 mL) solution of 4-(pivaloyloxy)benzaldehyde (1, 25 mg, 0.121 mmol) and trimethylcinnamylsilane (2, 46.7 mg, 0.245 mmol) was slowly added dropwise. After stirring overnight at room temperature, saturated sodium bicarbonate water (5 mL) was poured into the reaction mixture with vigorous stirring, diethyl ether (10 mL) was added and extraction was performed. Extractions were further carried out two times with diethyl ether (10 mL), the organic layers were combined, washed with a saturated sodium chloride aqueous solution (5 mL), dried with anhydrous magnesium sulfate, and concentrated. The residue was purified by thin layer chromatography (hexane:methylene chloride:diethyl ether=4:1:1), and the subject compound (4, 37.7 mg) was obtained as a colorless oily substance (yield 75%, syn/anti mixture).
