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) is added at 0°-5° to a stirred suspension of 5-amino-2,3-dimethoxy-1,4-naphthoquinone (233 mg, 1 mmol) in 0.6 N hydrochloric acid (10 ml) and tetrahydrofuran (1 ml). The mixture is stirred at 5° for 10 minutes until a clear solution is obtained and is then neutralized by the addition of sodium carbonate. The ice cold solution is then slowly added to a vigorously stirred two-phase mixture in a nitrogen atmosphere at 50° 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 is partitioned between ethyl acetate (40 ml) and brine (100 ml). The ethyl acetate phase is dried over MgSO4 and concentrated in vacuo. The residue is 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, affords 70 mg of 2,3-dimethoxy-5-phenylthio-1,4-naphthoquinone, mp 76°-77°.
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