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

참여 물질

반응 단계

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 (4.90 g, 96%), which was of sufficient purity (TLC analysis, 10% EtOAc, 90% CHCl3) for further reaction. The crude 17 was combined with trans-2-methyl-1,3-pentadiene (25 mL, technical, 75%, 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 20 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 an orange solid (9.3 g). TLC analysis (10% EtOAc, 90% CHCl3) showed no remaining 17. Without purification, the solid was dissolved in MeOH (400 mL, a gummy colorless solid (polymer?) failed to dissolve and was removed by filtration), Et3N (3 mL) added, and the resulting dark solution was allowed to vigorously stir under O2 for 2.5 h at it. 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 (5.9 g). Crystallization from 95% EtOH (170 mL) yielded 34 as yellow needles (2.79 g, 35% from 37, pure by TLC and

출처 및 근거