Site-Selective Electrochemical C-H Cyanation of Indoles.

Nitrogen-containing compounds are ubiquitously found in the fields of organic chemistry, pharmaceuticals, agrochemicals, medicinal chemistry and functional materials. The C—H bond amination reaction is one of the most straightforward protocols in the C—N bond formation, showing "step" and "atomic" economy. As a catalyst for C—H amination reaction, copper exhibits its unique catalytic properties due to easily accessible oxidation states. The research progress of copper-catalyzed C—H amination in recent years is summarized. At the same time, reaction mechanisms are also briefly described in representative aminations to provide insights for the development prospects of highly practical and more environmentally benign processes. 

Copper‐Mediated
 and Catalyzed
 C‐H
 Bond Amination via
 Chelation‐Assistance
 : Scope, Mechanism and Synthetic Applications

Cyanation of benzylic C–N bonds is useful in the preparation of important α-aryl nitriles. The first general catalytic cyanation of α-(hetero)aryl amines, analogous to the Sandmeyer reaction of anilines, was developed using reductive cyanation with CO2/NH3. A broad array of α-aryl nitriles was obtained in high yields and regioselectivity by C–N cleavage of intermediates as ammonium salts. Good tolerance of functional groups such as ethers, CF3, F, Cl, esters, indoles, and benzothiophenes was achieved. Using 13CO2, a 13C-labeled tryptamine homologue (five steps, 31% yield) and Cysmethynil (six steps, 37% yield) were synthesized. Both electronic and steric effects of ligands influence the reactivity of alkyl nickel species with electrophilic silyl isocyanates and thus determine the reactivity and selectivity of the cyanation reaction. This work contributes to the understanding of the controllable activation of CO2/NH3 and provides the promising potential of the amine cyanation reaction in the synthesis of bio-relevant molecules.

Catalytic Cyanation of C–N Bonds with CO2/NH3

Construction of a carbon-nitrogen bond is one of the most prevalent operations in nature and organic synthesis. The resulting amino compounds are privileged structural fragments in natural products, pharmaceutical drugs, and functional materials. With the rapid advancement of C-H bond activation, directing-group strategies in C-H amination catalyzed by rhodium have emerged. This reaction approach considerably enhances the step economy and atom economy of the reaction, and it complies with green chemistry and atom economy. The reactivity and selectivity of chelation-assisted rhodium-catalyzed C-H amination are discussed in relation to the types of aminating reagent, as well as the challenges and future development prospects in this field.

Directing group strategies in rhodium-catalyzed C-H amination.

In this update, we developed a mild, efficient and practical method using fluorosulfuryl imidazolium salt A as an environment friendly promoter for conversion of oximes to nitriles or amides via β-elimination or Beckmann rearrangement in almost quantitative yield in 10 minutes. The target products were generated in gram-scale and could be collected through crystallization without silica gel column purification in excellent yield.

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Xiao-Qiang Hu

Papers

Directing group strategies in catalytic sp2 C–H cyanations: scope, mechanism and limitations