N[C:2]1[O:6][N:5]=[C:4]([C:7]([O:9][CH2:10][CH3:11])=[O:8])[C:3]=1[C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1.N([O-])=O.[Na+]>C(O)(=O)C.O.O1CCCC1>[C:12]1([C:3]2[C:4]([C:7]([O:9][CH2:10][CH3:11])=[O:8])=[N:5][O:6][CH:2]=2)[CH:13]=[CH:14][CH:15]=[CH:16][CH:17]=1In an analogous manner to that described in J. Org. Chem. 50 (13) 1985, 2372-2375, 7.6 g (32.72 mmol) of ethyl 5-amino-4-phenyl-3-isoxazolecarboxylate in 160 ml of glacial acetic acid, 50 ml of water and 80 ml of tetrahydrofuran were treated portionwise at 15°-20° while stirring within 1 hour with a total of 22.6 g of sodium nitrite. The reaction mixture was thereafter poured into 1 liter of water and extracted 3 times with 400 ml of methylene chloride each time. The organic phases were combined and first washed twice with 1 liter of saturated sodium bicarbonate solution each time and then once with 1 liter of water, dried, filtered and concentrated in a vacuum, whereby after chromatography on silica gel and elution with methylene chloride there were obtained 3.9 g (55%) of ethyl 4-phenyl-3-isoxazolecarboxylate as a yellow oil which was used without further purification.
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