Benzoxazole → methoxy-benzoxazole
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[O:1]1[C:5]2[CH:6]=[CH:7][CH:8]=[CH:9][C:4]=2[N:3]=[CH:2]1.Br[C:11]1[O:12]C2C=CC=CC=2N=1.C[O-].[Na+]>CN(C=O)C.[Cu]Br>[CH3:11][O:12][C:2]1[O:1][C:5]2[CH:6]=[CH:7][CH:8]=[CH:9][C:4]=2[N:3]=1[O:1]1[C:5]2[CH:6]=[CH:7][CH:8]=[CH:9][C:4]=2[N:3]=[CH:2]1.Br[C:11]1[O:12]C2C=CC=CC=2N=1.C[O-].[Na+]>CN(C=O)C.[Cu]Br>[CH3:11][O:12][C:2]1[O:1][C:5]2[CH:6]=[CH:7][CH:8]=[CH:9][C:4]=2[N:3]=1In Scheme VIII, bromobenzoxazole 35 (R=CH3) was first treated with copper(I) cyanide in DMF to produce the corresponding aryl-nitrile, which upon treatment with boron tribromide afforded benzoxazole 36. Benzoxazole 36 was also prepared from a second synthetic Route, where the bromo-benzoxazole 35 was treated with zinc cyanide in the presence of a palladium catalyst [i.e. tetrakis(triphenylphosphine)palladium(0)] to afford the corresponding aryl-nitrile, which upon demethylation with boron tribromide produced benzoxazole 36. Benzoxazole 35 (R=H) was treated with copper (I) bromide, and freshly prepared sodium methoxide in DMF to produce methoxy-benzoxazole 37. Bromination of 37 with N-bromosuccinimide in acetonitrile afforded the monobromo benzoxazole 38 (major product) and the dibromobenzoxazole 39 (minor product).
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