Palladium‐Catalyzed sp 2 C−H Arylation of Azoarenes with Arylhydrazines

Transition‐metal‐catalyzed direct functionalization of C−H bonds is important for new compound synthesis, but usually needs special reagents and harsh conditions. With the aid of an azo directing group, the palladium‐catalyzed ortho ‐sp 2 C−H bond activation of azoarenes with hydrazines has been explored. In the reaction, the Pd catalyst reacts with azobenzene to form a palladacyclic intermediate, which reacts with a phenyl radical generated from phenylhydrazine under heating and oxygen to produce a Pd IV or Pd III intermediate. This finally undergoes reductive elimination to give the ortho ‐arylated products with the release of the Pd II catalyst. This reaction provides a novel access to ortho ‐aryl azoarenes under mild conditions in high yield.