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

関与物質

反応手順

To a vigorously stirred solution of NaIO4 (25.1 g, 117.5 mmol, Baker) in water (800 mL), there was added solid 2-methoxyhydroquinone (37, 5.20 g, 37.1 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 (4.80 g, 94%), which was of sufficient purity (TLC analysis, 10% EtOAc, 90% CHCl3) for further reaction. The crude quinone was combined with 2,3-dimethyl-1,3-butadiene (9.3 mL, Aldrich, used as received), toluene (50 mL) and hydroquinone (500 mg, Mallinkrodt). The reaction mixture was heated under N2 in a 60° C. oil bath for 17 h, with the contents being stirred magnetically. A pale orange, near homogeneous solution was present. The reaction was allowed to cool to rt, the contents filtered and the solvent removed in vacuo to give a brown solid (8.1 g). TLC analysis (10% EtOAc, 90% CHCl3) showed no remaining 17. Without purification, the solid was dissolved in MeOH (500 mL, a gummy colorless solid (polymer?) failed to dissolve and was removed by filtration), Et3N (4 mL) added, and the resulting dark solution was allowed to vigorously stir under O2 for 3.0 h at rt. TLC analysis (10% EtOAc, 90% CHCl3) showed the major Diels-Alder adduct to be consumed, with a major higher Rf spot being formed. The reaction mixture was acidified with 10% HCl (100 mL), diluted with H2O (200 mL) and the MeOH removed in vacuo to give an orange suspension. The suspension was extracted with CHCl3 (3×100 mL). The extract was washed with saturated NaHCO3 (3×75 mL), and H2O (1×200 mL), filtered through cotton, and the solvent removed in vacuo to give an orange solid (5.1 g). Crystallization from 95% EtOH (100 mL) yielded the product as yellow needles (2.27 g, 35% from 2-methoxyhydroquinone, 90% pure by TLC and 1H NMR). Further crystallization from 95% EtOH failed to improve the purity; mp 161.5°-162.5° C. (EtOH), lit. (Trave et al., Chim. e ind. (Milan) 41:19-29 (1959)) 166° C.; 1H NMR (CDCl3) δ2.39 (s, 6H), 3.88 (s, 3H), 6.10 (s, 1H), 7.82 (s, 1H), 7.88 (s, 1H). Note: The impurity is probably 2-methoxy-5,8-dihydro-6,7-dimethylnaphthalene-1,4-dione.

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