Transition metal-catalyzed direct functionalization of C–H bonds is one of the key emerging strategies that is currently attracting tremendous attention with the aim to provide alternative environmentally friendly and efficient ways for the construction of C–C and C–hetero bonds. In particular, the strategy involving regioselective C–H activation assisted by various functional groups shows high potential, and significant achievements have been made in both the development of novel reactions and the mechanistic study. In this review, we attempt to give an overview of the development of utilizing the functionalities as directing groups. The discussion is directed towards the use of different functional groups as directing groups for the construction of C–C and C–hetero bonds via C–H activation using various transition metal catalysts. The synthetic applications and mechanistic features of these transformations will be discussed, and the review is organized on the basis of the type of directing groups and the type of bond being formed or the catalyst.

Transition metal-catalyzed C–H bond functionalizations by the use of diverse directing groups

Oxidative Coupling between Two Hydrocarbons: An Update of Recent C–H Functionalizations

The development of mild and general methods for C–S bond formation has received significant attention because the C–S bond is indispensable in many important biological and pharmaceutical compounds. Early examples for the synthesis of C–S bonds are generally limited to the condensation reaction between a metal thiolate and an organic halide. Recent chemical approaches for C–S bond formation, based upon direct C–H bond functionalization and decarboxylative reactions, not only provide new insights into the mechanistic understanding of C–S coupling reactions but also allow the synthesis of sulfur-containing compounds from more effective synthetic routes with high atom economy. This review intends to explore recent advances in C–S bond formation via C–H functionalization and decarboxylation, and the growing opportunities they present to the construction of complex chemical scaffolds for applications encompassing natural product synthesis, synthetic methodology development, and functional materials as well as nanotechnology.

Recent advances in C–S bond formation via C–H bond functionalization and decarboxylation

Reported herein is the metal-catalyzed regioselective C–H functionalization of quinoline N-oxides at the 8-position: direct iodination and amidation were developed using rhodium and iridium catalytic systems, respectively. Mechanistic study of the amidation revealed that the unique regioselectivity is achieved through the smooth formation of N-oxide-chelated iridacycle and that an acid additive plays a key role in the rate-determining protodemetalation step. While this approach of remote C–H activation using N-oxide as a directing group could readily be applied to a wide range of heterocyclic substrates under mild conditions with high functional group tolerance, an efficient synthesis of zinquin ester (a fluorescent zinc indicator) was demonstrated.

Regioselective Introduction of Heteroatoms at the C-8 Position of Quinoline N-Oxides: Remote C–H Activation Using N-Oxide as a Stepping Stone

Rhodium(III)-Catalyzed C–C Bond Formation of Quinoline N-Oxides at the C-8 Position under Mild Conditions

Sulfonylation of quinoline N-oxides with aryl sulfonyl chlorides via copper-catalyzed C-H bonds activation.

An efficient and concise one-pot strategy for the direct alkylation of quinoline N-oxides via palladium-catalyzed dual CH bonds activation has been developed. This methodology provides quinoline-containing heterocyclic molecules in moderate to excellent yields.

Direct C-2 Alkylation of Quinoline N-Oxides with Ethers via Palladium-Catalyzed Dehydrogenative Cross-Coupling Reaction

Determination of optimum humidity for air-curing of cigar tobacco leaves during the browning period

Synthesis, thermal property and antifungal evaluation of pyrazine esters

An efficient protocol for preparation of sulfonylated quinoline N-oxides via Cu-catalyzed C—H bond activation is developed.

Zhiyong Wu

Papers

Sulfonylation of quinoline N-oxides with aryl sulfonyl chlorides via copper-catalyzed C-H bonds activation.

Direct C-2 Alkylation of Quinoline N-Oxides with Ethers via Palladium-Catalyzed Dehydrogenative Cross-Coupling Reaction

Determination of optimum humidity for air-curing of cigar tobacco leaves during the browning period

Synthesis, thermal property and antifungal evaluation of pyrazine esters

Sulfonylation of Quinoline N‐Oxides with Aryl Sulfonyl Chlorides via Copper‐Catalyzed C—H Bonds Activation.