Research and industrial interest in radical C–H activation/radical cross-coupling chemistry has continuously grown over the past few decades. These reactions offer fascinating and unconventional approaches toward connecting molecular fragments with high atom- and step-economy that are often complementary to traditional methods. Success in this area of research was made possible through the development of photocatalysis and first-row transition metal catalysis along with the use of peroxides as radical initiators. This Review provides a brief and concise overview of the current status and latest methodologies using radicals or radical cations as key intermediates produced via radical C–H activation. This Review includes radical addition, radical cascade cyclization, radical/radical cross-coupling, coupling of radicals with M–R groups, and coupling of radical cations with nucleophiles (Nu).

Recent Advances in Radical C-H Activation/Radical Cross-Coupling.

Recent Advances in Transition-Metal-Catalyzed Functionalization of Unstrained Carbon–Carbon Bonds

The exponential increase in the number of catalytic transformations that involve a metal-promoted activation of hitherto considered inert C−H bonds is promoting a fundamental change in the field of synthetic chemistry. Although most reactions involving C−H activations consist of simple functionalizations or additions, recent years have witnessed an upsurge in related transformations that can be formally considered as cycloaddition processes. These transformations are particularly appealing from a synthetic perspective because they allow the conversion of readily available substrates into highly valuable cyclic products in a rapid and sustainable manner. In many cases, these annulations involve the formation of metallacyclic intermediates that resemble those proposed for standard metal-catalyzed cycloadditions of unsaturated precursors.

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Metal-Catalyzed Annulations through Activation and Cleavage of C-H Bonds.

Recent advances in transition metal-catalyzed C–H bond functionalization have profoundly impacted synthetic strategy Since organic substrates typically contain several chemically distinct C–H bonds, controlling the regioselectivity of C–H bond functionalization is imperative to harness its full potential Moreover, the ability to alter reaction pathways to selectively functionalize different C–H bonds in a substrate represents a greater opportunity and challenge The choice of catalysts, ligands, solvents, and even more subtle variations of the reaction conditions have been shown to allow the formation of regioisomeric C–H functionalization products starting from the same precursors This review describes recent advances in transition metal-catalyzed divergent C–H bond functionalization that highlight its potential in organic synthesis

Transition metal-catalyzed site- and regio-divergent C–H bond functionalization

https://pubs.rsc.org/en/content/articlepdf/2014/cc/c3cc47081d

Aerobic oxidation catalysis with stable radicals

The palladium-catalyzed synthesis of benzofurans and coumarins by reacting phenols and unactivated olefins is described.

Palladium-Catalyzed Synthesis of Benzofurans and Coumarins from Phenols and Olefins†

Nitroolefin is a common and versatile reagent Its synthesis from olefin is generally limited by the formation of mixture of cis and trans compounds Here we report that silver nitrite (AgNO2) along with TEMPO can promote the regio- and stereoselective nitration of a broad range of olefins This work discloses a new and efficient approach wherein starting from olefin, nitroalkane radical formation and subsequent transformations lead to the desired nitroolefin in a stereoselective manner

Efficient and Stereoselective Nitration of Mono- and Disubstituted Olefins with AgNO2 and TEMPO

Stereoselective Nitration of Olefins with tBuONO and TEMPO: Direct Access to Nitroolefins under Metal-free Conditions

A palladium-catalyzed dehydrogenative coupling between diarylamines and olefins has been discovered for the synthesis of substituted indoles. This intermolecular annulation approach incorporates readily available olefins for the first time and obviates the need of any additional directing group. An ortho palladation, olefin coordination, and β-migratory insertion sequence has been proposed for the generation of olefinated intermediate, which is found to produce the expected indole moiety.

Palladium-catalyzed annulation of diarylamines with olefins through C-H activation: direct access to N-arylindoles.

Ferric nitrate with catalytic TEMPO has been identified as a useful reagent for regio- and stereoselective nitration of a wide variety of aromatic, aliphatic, and heteroaromatic olefins. This reaction provided nitroolefins in preparatively useful yields with excellent E-selectivity. Due to its mild nature and operational simplicity, the present protocol is expected to find application in synthetic setup.

Togati Naveen

Papers

Palladium-Catalyzed Synthesis of Benzofurans and Coumarins from Phenols and Olefins†

Efficient and Stereoselective Nitration of Mono- and Disubstituted Olefins with AgNO2 and TEMPO

Stereoselective Nitration of Olefins with tBuONO and TEMPO: Direct Access to Nitroolefins under Metal-free Conditions

Palladium-catalyzed annulation of diarylamines with olefins through C-H activation: direct access to N-arylindoles.

A predictably selective nitration of olefin with Fe(NO3)3 and TEMPO.