ortho‐Olefination of Arylaldehyde O‐Methyloximes through Palladium‐Catalyzed C–H Activation

Abstract

Palladium(II)‐catalyzed ortho‐olefination of arylaldehyde O‐methyloximes by using O‐methyloxime as a directing group gave 2‐alkenylarylaldehyde O‐methyloximes in moderate to good yields. After various reaction parameters (catalyst, oxidant, solvent, and reaction temperature) were examined, the optimal conditions for the reaction were identified. 2‐Alkenylarylaldehydes could be obtained conveniently by hydrolysis of the coupling products. The kinetic isotope effect (kH/kD) for the C–H bond activation was provided, and the possible mechanism of the reaction was proposed.

Oxidative Coupling between Two Hydrocarbons: An Update of Recent C–H Functionalizations

“…Other N -coordinating directing groups such as imine, amide, and amino have also been developed for various aromatic C–H alkenylations. As compared to sp 2 -hybrid N -ligand, O -ligand has a relatively weak coordination ability to palladium; those weak coordination ligands provide good directing property, yet meanwhile leave the catalyst center electrophilic enough for C–H palladation to occur.…”

Palladium-Catalyzed ortho–C-H Arylation of Acetophenone Oxime Ethers with Aryl Pinacol Boronic Esters

“…Synthesis of biaryl compounds has consistently been of great interest in organic synthesis, due to their wide array of applications in pharmaceuticals and agrochemicals . Various directing groups has been employed for palladium-catalyzed arylation of ortho -aromatic C–H bonds to synthesize biaryl motifs . Direct C–H arylation of O -methyl oximyl group has also been accomplished by using aryl iodides, aryldiazonium salts, diaryliodonium salts, acylperoxides, and arenes as the coupling partners …”

Palladium-Catalyzed meta-C–H Functionalization of Masked Aromatic Aldehydes

“…Our initial investigations aimed at utilizing imine-based directing groups to initiate our desired catalysis. Sun and coworkers have developed a palladium-catalyzed ortho-C−H olefination of aryl-aldoximes, 11 and the Takemoto group has developed a palladium-catalyzed annulation of aryl ketoximes with norbornene, 12 albeit in poor yields after long reaction times. Despite the precedent laid forth by these works, we were unable to observe significant meta-C−H functionalization with any of the imines that we employed in our studies.…”