Cu(II)-Catalyzed Synthesis of Benzoxazoles from Bisaryloxime Ethers

Significance

Reported is a new Cu(II)-catalyzed rearrangement of bisaryloxime ethers 1 into 2-arylbenzoxazoles 2 in the presence of oxygen. ­After screening of copper sources, solvent and loading, it was established that the optimal conditions require the presence of Cu(OTf)₂ (10 mol%) in a non-polar solvent (toluene). The scope of this reaction was extended to various bisaryloxime ethers 1 bearing EWGs and EDGs on Ar providing the corresponding benzoxazoles 2 in good yields. However, alkyl aryloxime ethers were shown not to undergo the rearrangement reaction. The structure of the benzoxazole product was established by X-ray crystal structure determination. A plausible mechanism was proposed without evidence.