[CH3:1][C:2]1[N:6]=[C:5]([C:7]2[CH:16]=[CH:15][C:10]([C:11]([O:13]C)=[O:12])=[CH:9][CH:8]=2)[O:4][N:3]=1.[OH-].[Li+]>O1CCOCC1.O.C(O)(C)C>[CH3:1][C:2]1[N:6]=[C:5]([C:7]2[CH:16]=[CH:15][C:10]([C:11]([OH:13])=[O:12])=[CH:9][CH:8]=2)[O:4][N:3]=1Methyl 4-(3-methyl-1,2,4-oxadiazol-5-yl)benzoate (J. R. Young and R. J. DeVita, Tetrahedron Lett., 1998, 39, 3931) was dissolved in a mixture of dioxan (110 ml), water (70 ml) and isopropanol (30 ml), and lithium hydroxide (1.38 g) was added. The mixture was stirred at room temperature for ca 5 h and then the mixture was acidified to ca pH 4 by addition of Amberlyst 15 H+ resin. The resin was removed by filtration and the filtrate was concentrated in vacuo. The solid white precipitate which was obtained was collected by filtration, washed with water on the filter and dried in vacuo at 40° C. for 48 h to give the title compound (D18) (4.23 g).
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