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

Abstract

In this Article, we report our successful attempt on the Pd(II)-catalyzed, bidentate directing group-aided, chemoselective acetoxylation/substitution of remote ε-C(sp)-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(sp)-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) in the presence of the Pd(OAc) 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.

Palladium‐Catalyzed 8‐Aminoquinoline‐Aided sp2δ‐C−H Intramolecular Amidation/Annulation: A Route to Tricyclic Quinolones

“…of TEMPO, which gave the product 20 a in 67% yield (Scheme ). In concurrence with the literature reports, this reaction indicated that perhaps the sp 2 δ ‐C−H intramolecular amidation/annulation of the substrates 12 and 19 did not proceed via the single electron transfer (SET) or free radical pathway …”

“…of PIDA and Pd[OAc] 2 (5 mol%) found to afford the thieno[2,3‐ c ]quinolin‐4(5 H )‐one derivative 20 a in a maximum of 94% yield (entry 2, Table ). It is to be noted that the C(2)/C(5)‐H bond of thiophene/furan systems is known to undergo the direct C−H functionalization (e. g., arylation and acetoxylation) . However, the other possible by‐product e. g., the C−H acetoxylated product 21 was not obtained from 19 a under the present experimental conditions.…”

“…Daugulis, Chen, Zhao and our group revealed the intramolecualr amidation/annulation of the remote sp 2 ϵ ‐C−H bond of benzylamine substrates 3 b (Scheme ). The C−H amidation/annulation of 3 b plausibly proceeded via a 7‐membered palladacycle intermediate ( III ) .…”

N‐Directed Pd‐Catalyzed Direct ortho‐Acetoxylation and ortho‐tert‐Butoxylation of 2‐Phenyl‐4H‐benzo[d][1,3]oxazin‐4‐ones via C‐H Activation

“…Moreover, functional group assisted selective acetoxylation of inert C−H bonds of an aryl system with the help of transition metal catalyst has proven to be a highly diligent approach for the direct construction of C−O bonds …”

“…[32][33][34][35][36][37][38][39][40][41][42] Moreover, functional group assisted selective acetoxylation of inert CÀ H bonds of an aryl system with the help of transition metal catalyst has proven to be a highly diligent approach for the direct construction of CÀ O bonds. [43][44][45][46][47][48][49][50][51] Taking an impetus from the enduring development of selective acetoxylation of CÀ H bonds and following our interest for the selective functionalization of valuable heterocyclic organic molecules (Scheme 1), [52][53]…”