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 n N→ π∗ C=Odelocalization in amides and n O→ π∗ C=Odonation 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 Introduction 2 Transamidation of Amides 2.1 Transamidation by Metal-NHC Catalysis (Pd-NHC, Ni-NHC) 2.2 Transition-Metal-Free Transamidation via Tetrahedral Intermediates 2.3 Reductive Transamidation 2.4 New Acyl-Transfer Reagents 2.5 Tandem Transamidations 3 Amidation of Esters 3.1 Amidation of Esters by Metal-NHC Catalysis (Pd-NHC, Ni-NHC) 3.2 Transition-Metal-Free Amidation of Esters via Tetrahedral Intermediates 3.3 Reductive Amidation of Esters 4 Transamidations of Amides by Other Mechanisms 5 Conclusions and Outlook.
All Science Journal Classification (ASJC) codes
- Organic Chemistry