Ligand‐Controlled Direct γ‐C−H Arylation of Aldehydes

The first example of Pd^II‐catalyzed γ‐C(sp³)?H functionalization of aliphatic and benzoheteroaryl aldehydes has been developed using a transient ligand and an external ligand, concurrently. A wide array of γ‐arylated aldehydes were readily accessed without preinstalling internal directing groups. The catalytic mechanism was studied by performing deuterium‐labelling experiments, which indicated that the γ‐C(sp³)?H bond cleavage is the rate‐limiting step during the reaction process. This reaction could be performed on a gram scale, and also demonstrated its potential application in the synthesis of new mechanofluorochromic materials with blue‐shifted mechanochromic properties.