NaIO4 (3 g, 14 mmol) was added to a suspension of DCM (30 mL) containing silica (10 g), followed by the addition of olefin 9 (355 mg, 2 mmol) pre-dissolved in DCM (20 mL). The reaction mixture was stirred at room temperature for 30 min and then filtered. The solid residue was washed twice with DCM (20 mL). The combined organic phases were dried with MgSO4, filtered and concentrated under reduced pressure under strictly controlled conditions (20 °C, 300 mmHg) to avoid loss of aldehyde 10 due to high volatility. A clear liquid-like crude product (350 mg, 85% yield) was finally obtained, which was directly used in the subsequent reaction without further purification.1H NMR (400 MHz, CDCl3): δ= 9.47 (d, J = 1.5 Hz, 1H, 1-H), 4.50 (d, J = 1.5 Hz, 1H, 2-H), 3.46 (s, 6H, 3-H) ppm. 13C NMR (100 MHz, CDCl3): δ= 199.2 (1-C), 122.3 (2-C), 54.6 (3-C) ppm.
