N[C:2]1[C:3]([O:15][CH3:16])=[CH:4][C:5]2[C:9]3[CH:10]=[CH:11][CH:12]=[CH:13][C:8]=3[O:7][C:6]=2[CH:14]=1.S(=O)(=O)(O)O.N([O-])=O.[Na+].S(=O)(=O)(O)N.[C:31]([OH:35])(=[O:34])[CH2:32][SH:33]>C(O)(=O)C.O.C(=O)([O-])[O-].[Cu+2].C(OCC)(=O)C>[CH3:16][O:15][C:3]1[C:2]([S:33][CH2:32][C:31]([OH:35])=[O:34])=[CH:14][C:6]2[O:7][C:8]3[CH:13]=[CH:12][CH:11]=[CH:10][C:9]=3[C:5]=2[CH:4]=13-Amino-2-methoxydibenzofuran (10 g, 46.9 mmol) was stirred in a mixture of acetic acid (100 ml), water (120 ml) and concentrated sulphuric acid (23.5 ml) at 80° C. for 15 minutes. The mixture was cooled to 0° C. and a solution of sodium nitrite (3.9 g, 57 mmol) in water (15 ml) was added at such a rate that the temperature did not exceed 4° C. The mixture was cooled -5° C. After 15 minutes, the excess sodium nitrite was decomposed by addition of an excess of sulphamic acid (0.9 g). The solution of the diazonium salt was added in a steady stream to a stirred mixture of basic copper carbonate (2.9 g) in water (50 ml) at 0° C. to which had been added thioglycolic acid (4.1 ml, 59 mmol). The mixture was allowed to attain ambient temperature during 30 minutes and then stirred thus for 4.5 hours until gas evolution (nitrogen) had ceased. Ethyl acetate (100 ml) was then added and solid material removed by filtration through diatomaceous earth, washing the filter pad with ethyl acetate. The organic layer was separated from the filtrate and washings extracted with 2 M aqueous sodium hydroxide solution (7×100 ml). Those extracts containing product [as indicated by thin layer chromatography (tlc) of a neutralised aliquot on silica, using ethyl acetate as eluant] were combined, washed with ether (100 ml), then neutralised with 2 M hydrochloric acid in the presence of ether (100 ml). This ether layer was separated, washed with brine and the solvent evaporated. Toluene was added to the residue and then removed by evaporation to remove remaining acetic acid. The residual yellow-brown solid was recrystallised from toluene to give 2-(2-methoxydibenzofuran-3-yl-thio)acetic acid (D) as a tan solid (2.60 g), m.p. 180°-182° C., which was used without further purification.
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