Benzoic acids are highly important structural motifs in drug molecules and natural products. Selective C–H bond functionalization of benzoic acids will provide synthetically useful tools for step-economical organic synthesis. Although direct ortho-C–H functionalizations of benzoic acids or their derivatives have been intensely studied, the ability to activate meta-C–H bond of benzoic acids or their derivatives in a general manner via transition-metal catalysis has been largely unsuccessful. Although chelation-assisted meta-C–H functionalization of electron-rich arenes was reported, chelation-assisted meta-C–H activation of electron-poor arenes such as benzoic acid derivatives remains a formidable challenge. Herein, we report a general protocol for meta-C–H olefination of benzoic acid derivatives using a nitrile-based sulfonamide template. A broad range of benzoic acid derivatives are meta-selectively olefinated using molecular oxygen as the terminal oxidant. The meta-C–H acetoxylation, product of which is further transformed at the meta-position, is also reported.
The trifluoroethyl aryl ethers are important motifs in drug molecules. However, a report devoted specifically to the study of transition-metal-catalyzed C-H trifluoroethoxylation has not been reported to date. A protocol of Pd(II)-catalyzed o-C-H trifluoroethoxylation of a broad range of benzoic acid derivatives (i.e., N-sulfonylbenzamides) has been developed. This method is also applied to the formal synthesis of the drug molecule flecainide, wherein the first m-C-H trifluoroethoxylation is also exemplified.
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