Palladium-catalyzed ortho-halogenation of diaryl oxime ethers

The palladium-catalyzed ortho monobromination and iodination of single E or Z geometric isomers of substituted diaryl ketoxime ethers [Ar1C(Ar2) = N–OCH3] have been accomplished in good yield (64–82% isolated yield). A minor amount of di-ortho-halogenation side product is produced in this reaction (0–10%). The aromatic ring that is halogenated is the one ‘trans’ to the OCH3 group, indicating that there is no isomerization about the CN bond during the reaction. Further, the site of functionalization is presumably controlled by the lone pair electrons on nitrogen. This study is the first to demonstrate the ability of the geometry of the oxime ether group to target the functionalization of only one aromatic ring when there are two aromatic rings directly attached to the carbon of the CN bond of the oxime ether. Electron-withdrawing substituents on either ring decrease reaction rate and diminish the amount of di-ortho-bromination side product.