[F:1][C:2]1[CH:7]=[CH:6][C:5]([C:8]2[CH:12]=[C:11]([OH:13])[NH:10][N:9]=2)=[CH:4][CH:3]=1.C([O-])([O-])=O.[K+].[K+].CS(O[CH:25]([CH:27](OS(C)(=O)=O)[CH3:28])[CH3:26])(=O)=O>CN(C=O)C.O>[F:1][C:2]1[CH:3]=[CH:4][C:5]([C:8]2[CH:12]=[C:11]3[O:13][CH:25]([CH3:26])[CH:27]([CH3:28])[N:10]3[N:9]=2)=[CH:6][CH:7]=1
To a solution of 3-(4-fluorophenyl)-1H-pyrazol-5-ol (3 g, 16.8 mmol) in DMF (15 mL) was added K2CO3 (9.3 g, 67.4 mmol) and butane-2,3-diyl dimethanesulfonate (4.8 g, 18.5 mmol) (prepared as described in US2010/41748) at room temperature and then stirred for 16 h at 60° C. Thereafter, the reaction mixture was diluted with cold water and extracted with ethyl acetate. The organic layer was dried over anhydrous sodium sulphate and concentrated to get the crude product. Purification by column chromatography over silica gel (eluent 5-10% ethyl acetate in petrol ether) yielded 6-(4-fluorophenyl)-2,3-dimethyl-2,3-dihydropyrazolo[5,1-b][1,3]oxazole (2.8 g, 71%) as yellow oil and a mixture of diastereoisomers.
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