[NH2:1][C:2]1[CH:7]=[C:6]([CH3:8])[C:5]([Br:9])=[CH:4][C:3]=1[OH:10].[Yb+3].FC(F)(F)S([O-])(=O)=O.FC(F)(F)S([O-])(=O)=O.FC(F)(F)S([O-])(=O)=O.[C:36](OC)(OC)(OC)[CH3:37]>CCO.CC(=O)OCC>[Br:9][C:5]1[C:6]([CH3:8])=[CH:7][C:2]2[N:1]=[C:36]([CH3:37])[O:10][C:3]=2[CH:4]=1A mixture of 2-amino-5-bromo-4-methylphenol (42) (290 mg), trifluoromethanesulfonic acid Ytterbium (III) salt (20 mg, 1% mol) and trimethyl orthoacetate (216 μl, 1.5 eq.) in 2 ml EtOH was heated at 90° C. for 2 h. After cooling down to r.t., the reaction mixture was taken up in EA, washed with aq. NaHCO3 and brine, dried over Na2SO4, concentrated to dryness. The resulting brown solid was dissolved in DCM and subjected to silica gel column purification using 0-60% B (A: hexane; B: 50% EA in hexane) to furnish 148 mg 6-bromo-2,5-dimethylbenzoxazole (48) as pale brown solid.
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