Non-Classical Amide Bond Formation: Transamidation and Amidation of Activated Amides and Esters by Selective N–C/O–C Cleavage

Abstract

In the past several years, tremendous advances have been made in non-classical routes for amide bond formation that involve transamidation and amidation reactions of activated amides and esters. These new methods enable the formation of extremely valuable amide bonds via transition-metal-catalyzed, transition-metal-free, or metal-free pathways by exploiting chemoselective acyl C–X (X = N, O) cleavage under mild conditions. In a broadest sense, these reactions overcome the formidable challenge of activating C–N/C–O bonds of amides or esters by rationally tackling nN → π*C=O delocalization in amides and nO → π*C=O donation in esters. In this account, we summarize the recent remarkable advances in the development of new methods for the synthesis of amides with a focus on (1) transition-metal/NHC-catalyzed C–N/C–O bond activation, (2) transition-metal-free highly selective cleavage of C–N/C–O bonds, (3) the development of new acyl-transfer reagents, and (4) other emerging methods.1 Introduction2 Transamidation of Amides2.1 Transamidation by Metal–NHC Catalysis (Pd–NHC, Ni–NHC)2.2 Transition-Metal-Free Transamidation via Tetrahedral Intermediates2.3 Reductive Transamidation2.4 New Acyl-Transfer Reagents2.5 Tandem Transamidations3 Amidation of Esters3.1 Amidation of Esters by Metal–NHC Catalysis (Pd–NHC, Ni–NHC)3.2 Transition-Metal-Free Amidation of Esters via Tetrahedral Intermediates3.3 Reductive Amidation of Esters4 Transamidations of Amides by Other Mechanisms5 Conclusions and Outlook

B2(OH)4-Mediated Reductive Transamidation of N-Acyl Benzotriazoles with Nitro Compounds En Route to Aqueous Amide Synthesis

“…However, the practitioners often need the assistance of some exotic or waste-intensive activators or coupling reagents to ensure efficient C–N bond formations . In the past few decades, nonclassic methods grow rapidly and thus offer many new options for constructing amide moieties . The direct acylation of amines by amides, a.k.a.…”

Ativação de Amidas – Um Instrumento Elegante para a Quimiosseletividade

“…Esquema 4 -Mecanismo geral de ativação de amidas por torção nas reações de acoplamento cruzado [14,15]. e a estrutura da 1-aza-2-adamantanona que continha uma ligação amida perfeitamente perpendicular [9].…”

“…Recentemente surgiu um interesse na ativação da ligação N-C(O) das amidas através da inserção seletiva de um metal na ligação N-C(O) (Esquema 4) [14,15]. O uso da torção na ligação amida permitiu o avanço da química orgânica em geral, sendo agora uma ligação C-N atrativa e com possibilidade de ser explorada em reações de acoplamento cruzado.…”

Decarboxylative Amidation of Aryl/Heteroarylacetic Acids via Activated Esters through Traceless α-Functionalized Benzylic Radicals

“…The anaerobic generation of benzyl radical, which is subsequently converted to activated ester by reaction with PINO, is suggested, excluding the role of oxygen in its formation (Scheme , part B). The decarboxylative amidation, in stark contrast to conventional amide synthesis, involves decarboxylation of the original carboxylic acid group, thereby making a synthon ready for amide synthesis, which differentiates these scaffolds from conventionally used aromatic acids and acid chlorides. Perhaps more importantly, decarboxylative amidation applicable to nonaromatic/heteroaromatic carboxylic acids largely remains unexplored.…”