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In an oven-dried, 500 mL round bottom flask equipped with a stir bar and an addition funnel, p-toluenesulfonic acid monohydrate (156 mg, 0.82 mmol), pyridine (66 μL, 0.82 mmol), acetovanillone (6.10 g, 36.7 mmol), and CH2Cl2 (170 mL) were combined and rapidly stirred. Dihydropyran (10 mL, 110 mmol) was diluted with 40 mL of CH2Cl2, poured into the addition funnel, and added drop wise to the acetovanillone solution over a period of 2 h. The reaction was stirred for an additional 12 h at room temperature, after which it was washed with 200 mL of 1.0 N NaOH (2×). The organic phase was dried over Na2SO4, filtered, and concentrated to a clear oil under reduced pressure. The oil crystallized upon standing to afford 4.2 g of THP-C as a white solid (46% yield). The solid was used without further purification. TLC: Rf=0.19 (hexane/EtOAc 4:1); Melting point: 67-69° C.; 1H NMR: (300 MHz, CDCl3) δ 7.52 (s, 1H), 7.50 (d, J=10 Hz, 1H), 7.13 (d, J=8 Hz, 1H), 5.50 (t, J=3 Hz, 1H), 3.90 (s, 3H), 3.89 (m, 1H), 3.59 (m, 1H), 2.54 (s, 3H), 1.95 (m, 3H), 1.63 (m, 1H); 13C NMR: (75 MHz, CDCl3) δ 197.08, 150.92, 150.12, 131.60, 123.18, 115.65, 111.29, 97.14, 62.31, 56.32, 30.33, 26.45, 25.31, 18.79; IR (ATR): 2966, 2936, 2880, 1672, 1585, 1510, 1462, 1442, 1413, 1390, 1352, 1290, 1272, 1243, 1221, 1201, 1172, 1153, 1120, 1110, 1051, 1032, 1020, 959 1046 cm−1; ESI-MS: expected, 250.1; observed, m/z 251.1 [M+H+].
