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A solution of 2,3-butanedione monooxime (50 g, 0.49 mol) and 4-bromobenzaldehyde (101 g, 0.54 mol) in acetic acid (500 mL) was cooled to 0° C. and then gaseous HCl was bubbled through the solution for 35 min while the reaction was stirred in an ice bath. Diethyl ether (500 mL) was then added to the reaction to precipitate the product and the resultant slurry stirred 45 min at 0° C. before being filtered. The solids were rinsed with Et2O (50 mL), taken up in water (1 L) and conc. NH4OH (60 mL) added to the slurry. This mixture was extracted with CHCl3, the organic layer was dried (MgSO4), and the solvent removed in vacuo to give 97.4 g (74%) of 2-(4-bromophenyl)-4,5-dimethyloxazole-3-oxide as a white solid. The compound should be used directly with 24-48 h: 1H NMR (500 MHz, CDCl3) δ 8.34 (d, J=9.0 Hz, 2H), 7.61 (d, J=9.0 Hz, 2H), 2.35 (s, 3H), 2.20 (s, 3H); 13C (125 MHz, CDCl3) δ 142.1, 131.9, 129.5, 126.3, 124.1, 122.2, 11.1, 6.2; IR (KBr) 1685, 1529, 1418, 1377, 1233, 1165 cm−1; UV (EtOH) λmax 307 nm (ε 24371); HRMS (TOF) m/z calc'd for C11H1179BrNO2: 267.997, found 267.9951.

1. customgaseous HCl was bubbled through the solution for 35 min while the reaction
2. additionDiethyl ether (500 mL) was then added to the reaction
3. customto precipitate the product
4. stirringthe resultant slurry stirred 45 min at 0° C.
5. filtrationbefore being filtered
6. washThe solids were rinsed with Et2O (50 mL)
7. additionconc. NH4OH (60 mL) added to the slurry
8. extractionThis mixture was extracted with CHCl3
9. dry with materialthe organic layer was dried (MgSO4)
10. customthe solvent removed in vacuo