2-Methoxybenzene-1,4-diol → 2-Methoxy-1,4-benzoquinone

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The procedure employed was a modification of that used by Okamato et al. (Chem. Pharm. Bull 32:4593-4599 (1984)). To a vigorously stirred solution of NaIO4 (15.4 g, 72.2 mmol, Baker) in water (500 mL), there was added solid 2-methoxyhydroquinone (37, 3.20 g, 22.8 mmol) in portions. The reaction immediately became dark orange. The reaction was allowed to stir for 1 h at rt and was extracted with CH2Cl2 (3×100 mL). The extract was washed with half saturated brine (1×100 mL), filtered through cotton and the solvent removed in vacuo to yield 17 as an orange solid (3.07 g, 97%), which was of sufficient purity (TLC analysis, 10% EtOAc, 90% CHCl3) for further reaction. The crude 17 was combined with hydroquinone (300 mg, Mallinkrodt), toluene (20 mL) and freshly distilled cyclopentadiene (15 mL, from the distillation of dicyclopentadiene, Aldrich). The reaction was allowed to stir at rt for 35 min at which point an orange homogeneous solution was present. TLC analysis (10% EtOAc, 90% CHCl3) indicated total conversion of the 2-methoxybenzoquinone to the lower Rf adduct. The lower boiling volatiles were removed in vacuo to give an orange liquid. Washing the liquid with ice cold hexanes yielded a beige solid (4.4 g). This was purified chromatographically (silica gel, 2.5×25 cm, CHCl3 elution) to yield an oil. Trituration with hexanes (50 mL), ice cold ether (3×10 mL) and hexanes (1×10 mL) yielded 46 as a pinkish powder (3.00 g, 64%, pure by TLC and 1H NMR); mp 95°-97° C., lit. (Okamato et al.) 97°-99.5° C.; 1H NMR (CDCl3) δ1.44 (d, J=9.0 Hz, 1H), 1.55 (m, 1H), 3.24 (m, 2H), 3.55 (m, 2H) 3.72 (s, 3H), 5.89 (s, 1H), 6.07 (m, 2H).

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