N([O-])=O.[Na+].N[C:6]1[CH:15]=[CH:14][CH:13]=[C:12]2[C:7]=1[C:8](=O)[C:9](OC)=[C:10](OC)[C:11]2=O.[C:22](=[O:25])([O-])[O-].[Na+].[Na+].[OH-:28].[K+].[C:30]1([SH:36])[CH:35]=[CH:34][CH:33]=[CH:32][CH:31]=1.[O:37]1[CH2:41]CCC1>Cl.C(OCC)(=O)C.O>[CH3:41][O:37][C:31]1[C:30](=[S:36])[C:35]2[C:34]([C:33](=[O:28])[C:32]=1[O:25][CH3:22])=[C:8]([C:7]1[CH:6]=[CH:15][CH:14]=[CH:13][CH:12]=1)[CH:9]=[CH:10][CH:11]=2Sodium nitrite (0.18 g) was added at 0°-5° C. to a stirred suspension of 5-amino-2,3-dimethoxy-1,4-naphthoquinone (233 mg, 1 mmol) in 0.6N hydrochloric acid (10 ml) and tetrahydrofuran (1 ml). The mixture was stirred at 5° C. for 10 minutes until a clear solution was obtained and was then neutralized by the addition of sodium carbonate. The ice cold solution was then slowly added to a vigorously stirred two-phase mixture in a nitrogen atmosphere at 50° C. composed of potassium hydroxide (0.16 g), water (10 ml), thiophenol (0.32 ml) and ethyl acetate (35 ml). After a total reaction time of 20 min, the mixture was partitioned between ethyl acetate (40 ml) and brine (100 ml). The ethyl acetate phase was dried over MgSO4 and concentrated in vacuo. The residue was purified by chromatography on a thick layer silica gel plate using acetone:toluene:chloroform (1:20:20) giving a solid that, after recrystallizing from isopropanol, afforded 70 mg of 2,3-dimethoxy-5-phenylthio-1,4-naphthoquinone, mp 76°-77° C.
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