3.1.2. Synthesis of 7-Hydroxy-2,2-dimethyl-2H-chromene-6-carbaldehyde 8

A mixture of compound 7 (1.0 g, 4.85 mmol) and DDQ (1.2 g, 5.28 mmol) in benzene (10 mL) was refluxed for 6 h, and the precipitate was filtered off. The filtrate was evaporated to dryness to afford the crude product, which was purified via column chromatography (silica gel, 10:1 hexane:EtOAc) to obtain a white solid of 7-hydroxy-2,2-dimethyl-2H-chromene-6-carbaldehyde 8 (0.91 g, 92% yield): m.p. 82–83 °C (lit. [20] 95–96 °C), ¹H NMR (300 MHz, CDCl₃): δ 11.41 (br, OH), 9.68 (s, 1H), 7.16 (s, 1H), 6.35 (s, 1H), 6.30 (d, J = 7.86 Hz, 1H), 5.59 (d, J = 9.93 Hz, 1H), 1.59 (s, 3H) 1.48 (s, 3H) ppm.