Recent Progress in the Construction of C−N Bonds via Metal‐Free Radical C(sp³)−H Functionalization

Abstract

Nitrogen‐containing compounds widely exist in pharmaceuticals and multifunctional materials. Thus, the development of C−N bond formation reactions is of great importance in synthetic chemistry. Since 2014, obvious progress has been made in the construction of C−N bonds via metal‐free radical C(sp3)−H functionalization, which is one of the major protocols due to its high reaction activity and mild conditions. To the best of our knowledge, there are still no exclusive reviews about the formation of C−N bonds through metal‐free radical C(sp3)−H functionalization. This review aims to highlight the recent advances in this area since 2014, according to the type of the nitrogen source (amines, amides, sulfonamides, azoles, azides and other nitrogen sources). The paper is focused on discussions about the reaction mechanisms and selected examples of substrates have also been listed.

One‐Pot Synthesis of Primary and Secondary Aliphatic Amines via Mild and Selective sp3 C−H Imination

“…Within that mechanistic framework, milder and more selective amine cyclization has recently been developed using triiodide‐catalysis and visible‐light activation, [14] while intermolecular sp 3 C−H amination using triflamide was reported (Scheme 1, middle) [15] . Nevertheless, the price of mild radical C−H amination remains the use of an activating group that must be removed in a separate step [16] …”

Iodine‐Catalyzed or ‐Mediated Reactions in Aqueous Medium

“…Conceptually, iodine is a mild oxidizing agent and can be used selectively in many organic syntheses. Before experiencing abundant iodine catalyzed organic synthetic methodology, the advantages of the use of iodine as compared to other halogens and transition metal catalysts are summarized below: [37–50] …”

“…[33][34][35][36] Conceptually, iodine is a mild oxidizing agent and can be used selectively in many organic syntheses. Before experiencing abundant iodine catalyzed organic synthetic methodology, the advantages of the use of iodine as compared to other halogens and transition metal catalysts are summarized below: [37][38][39][40][41][42][43][44][45][46][47][48][49][50] I. Like transition metal catalyst iodine also exists in different oxidation states such as À 1, 0, + 1, + 3, + 5 and + 7 in various inorganic and organic derivatives.…”

Metal‐Free Decarboxylation of α,β‐Unsaturated Carboxylic Acids for Carbon–Carbon and Carbon–Heteroatom Coupling Reactions

“…A series of admirable efforts have been done by many research groups. [49] Among them, the metal-free decarboxylative coupling of carboxylic acids represents a green and sustainable alternative. In 2006, Zhao and co-workers developed a novel decarboxylative strategy for the synthesis of 4,4-dialkylthio-1,2-diaza-1,3-butadienes via an azocoupling reaction of α-carboxy ketene dithioacetals with aryldiazonium salts (Scheme 23a).…”