Transition-metal-catalyzed acetoxylation of heterocycles: all that glitters is not palladium

Pd(II)-Catalyzed Bidentate Directing Group-Aided Chemoselective Acetoxylation of Remote ε-C(sp2)-H Bonds in Heteroaryl-Aryl-Based Biaryl Systems

In this Article, we report our successful attempt on the Pd(II)-catalyzed, bidentate directing group-aided, chemoselective acetoxylation/substitution of remote ε-C(sp2)-H bonds using heteroaryl-aryl-based biaryl systems. While the bidentate directing group (BDG)-aided, C-H activation, and functionalization/acetoxylation of the β-, γ-, and δ-C-H bonds of the appropriate carboxamide systems were well documented, there exist only rare reports dealing with the C-H activation and functionalization of remote ε-C-H bonds of appropriate substrates. Especially, the BDG-aided chemoselective acetoxylation of the remote ε-C(sp2)-H bond over cyclization has not been explored well. Accordingly, in this work, the treatment of various picolinamides/oxalylamides/pyrazine-2-carboxamides 4/7/9/11, which were derived from the corresponding C-3 arylated furfurylamines or thiophen-2-ylmethanamines with PhI(OAc)2 in the presence of the Pd(OAc)2 catalyst, successfully afforded the corresponding ε-C-H acetoxylated products. The chemoselective acetoxylation of the ε-C-H bond was possible and facilitated by the biaryl substrate 4/7/9/11 and not by the biaryl substrate 2a.