Carboxy Group as a Remote and Selective Chelating Group for C−H Activation of Arenes

Abstract

The first example of carboxy group assisted, remote‐selective C(sp2)−H activation with a PdII catalyst has been developed and proceeds through a possible κ2 coordination of the carboxy group, thus suppressing the ortho‐C−H activation through κ1 coordination. Besides meta‐C−H olefination, direct meta‐arylation of hydrocinnamic acid derivatives with low‐cost aryl iodides has been achieved for the first time. These findings may motivate the exploration of novel reactivities of the carboxy assisted C−H activation reactions with intriguing selectivities.

Hexafluoroisopropanol: the magical solvent for Pd-catalyzed C–H activation

“…48 Interestingly, the same legacy was followed when a carboxylate group was employed for the remote meta-selective olenation of hydrocinnamic amides by Li group in 2019. 49 This work describes the predominance of k 2 mode over k 1 mode (which was more facile for proximal ortho-functionalization due to right conformational orientation) of the carboxyl group for any remote C-H functionalization for the very rst time.…”

Palladium-catalyzed remote para-C–H activation of arenes assisted by a recyclable pyridine-based template

“… 13 Therefore, phenylpropionic acid was selected as the model substrate for our investigation of para -C–H activation of arenes. Based on our recent work on meta -C–H activation of phenylpropionic acid 14 and inspired by recent research on meta -C–H activation assisted by pyridine-based DTs, 12 we designed a series of potential pyridine-based para -DTs with different substitutions to attach with phenylpropionic acid, leading to the amide substrates ( Table 1 , see ESI † for more DTs evaluated), where the nitrogen atom of pyridine could coordinate to the transition metal to induce site-selective C–H activation. The design of the structure of the template was also inspired by previous reported nitrile-based biphenyl containing para -directing template.…”

Recent development in transition metal-catalysed C–H olefination

“…In 2019, Li and co-workers first discovered the carboxylic acid group as the directing auxiliary for meta- olefination ( Scheme 44 ). 52 The reaction proceeded through the assistance of the carboxylic acid group, which binds with Pd possibly through k 2 -coordination mode instead of k 1 thus overriding ortho -C–H activation. The reaction proceeded well with a series a substituted arenes 90 and different olefins including styrenes and delivered meta -olefinated products 91 in good yield and selectivity.…”