scholarly journals Transamidation of Amides and Amidation of Esters by Selective N–C(O)/O–C(O) Cleavage Mediated by Air- and Moisture-Stable Half-Sandwich Nickel(II)–NHC Complexes

Molecules ◽  
2021 ◽  
Vol 26 (1) ◽  
pp. 188
Author(s):  
Jonathan Buchspies ◽  
Md. Mahbubur Rahman ◽  
Michal Szostak
Keyword(s):  
Organic Synthesis ◽  
Bond Cleavage ◽  
Methyl Esters ◽  
Heterocyclic Carbenes ◽  
Amide Bond ◽  
Amide Bonds ◽  
Bond Forming ◽  
Cleavage Reactions ◽  
Metal Catalyzed ◽  
Half Sandwich

The formation of amide bonds represents one of the most fundamental processes in organic synthesis. Transition-metal-catalyzed activation of acyclic twisted amides has emerged as an increasingly powerful platform in synthesis. Herein, we report the transamidation of N-activated twisted amides by selective N–C(O) cleavage mediated by air- and moisture-stable half-sandwich Ni(II)–NHC (NHC = N-heterocyclic carbenes) complexes. We demonstrate that the readily available cyclopentadienyl complex, [CpNi(IPr)Cl] (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), promotes highly selective transamidation of the N–C(O) bond in twisted N-Boc amides with non-nucleophilic anilines. The reaction provides access to secondary anilides via the non-conventional amide bond-forming pathway. Furthermore, the amidation of activated phenolic and unactivated methyl esters mediated by [CpNi(IPr)Cl] is reported. This study sets the stage for the broad utilization of well-defined, air- and moisture-stable Ni(II)–NHC complexes in catalytic amide bond-forming protocols by unconventional C(acyl)–N and C(acyl)–O bond cleavage reactions.

Ultrasonically dispersed potassium in organic synthesis. Water-acceleration in reductive CS bond cleavage reactions

1991 ◽  
Vol 32 (29) ◽  
pp. 3551-3554 ◽  
Author(s):  
Ta-shue Chou ◽  
Shao-Hwa Hung ◽  
Man-Li Peng ◽  
Shwu-Jiaun Lee
Keyword(s):  
Organic Synthesis ◽  
Bond Cleavage ◽  
Cleavage Reactions

Activation of C–F, Si–F, and S–F Bonds by N-Heterocyclic Carbenes and Their Isoelectronic Analogues

Synlett ◽  
2020 ◽  
Vol 31 (14) ◽  
pp. 1349-1360 ◽  
Author(s):  
Eunsung Lee ◽  
Ewa Pietrasiak
Keyword(s):  
Nucleophilic Substitution ◽  
Organic Synthesis ◽  
Bond Activation ◽  
Bond Cleavage ◽  
Oxidative Addition ◽  
Main Group ◽  
Heterocyclic Carbenes ◽  
Full Potential ◽  
Short Summary ◽  
Special Case

Reactions involving C–F, Si–F, and S–F bond cleavage with N-heterocyclic carbenes and isoelectronic species are reviewed. Most examples involve activation of aromatic C–F bond via an SNAr pathway and nucleophilic substitution of fluorine in electron-deficient olefins. The mechanism of the C–F bond activation depends on the reaction partners and the reaction can proceed via addition–elimination, oxidative addition (concerted or stepwise) or metathesis. The adducts formed upon substitution find applications in organic synthesis, as ligands and as stable radical precursors, but in most cases, their full potential remains unexplored.1 Introduction1.1 The C–F Bond1.2 C–F Bond Activation: A Short Summary1.3 C–F Bond Activation: A Special Case of SNAr1.4 N-Heterocyclic Carbenes (NHCs)1.5 The Purpose of this Article2 C–F bond Activation in Acyl Fluorides3 Activation of Vinylic C–F Bonds4 Activation of Aromatic C–F Bonds5 X–F Bond Activation (X = S or Si)6 C–F Bond Activation by Main Group Compounds Isoelectronic with NHCs7 Conclusions and Outlook

Amide Synthesis by Transamidation of Primary Carboxamides

Synthesis ◽  
2020 ◽  
Vol 52 (21) ◽  
pp. 3231-3242
Author(s):  
Sylvain Laclef ◽  
Maria Kolympadi Marković ◽  
Dean Marković
Keyword(s):  
Synthetic Methods ◽  
Amide Bond ◽  
Industrial Chemistry ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Atom Economy ◽  
Bond Forming ◽  
Effective Strategies ◽  
Brönsted Acid ◽  
Metal Catalyzed

The amide functionality is one of the most important and widely used groups in nature and in medicinal and industrial chemistry. Because of its importance and as the actual synthetic methods suffer from major drawbacks, such as the use of a stoichiometric amount of an activating agent, epimerization and low atom economy, the development of new and efficient amide bond forming reactions is needed. A number of greener and more effective strategies have been studied and developed. The transamidation of primary amides is particularly attractive in terms of atom economy and as ammonia is the single byproduct. This review summarizes the advancements in metal-catalyzed and organocatalyzed transamidation methods. Lewis and Brønsted acid transamidation catalysts are reviewed as a separate group. The activation of primary amides by promoter, as well as catalyst- and promoter-free protocols, are also described. The proposed mechanisms and key intermediates of the depicted transamidation reactions are shown.1 Introduction2 Metal-Catalyzed Transamidations3 Organocatalyzed Transamidations4 Lewis and Brønsted Acid Catalysis5 Promoted Transamidation of Primary Amides6 Catalyst- and Promoter-Free Protocols7 Conclusion

scholarly journals Fast Amide Bond Cleavage Assisted by a Secondary Amino and a Carboxyl Group—A Model for yet Unknown Peptidases?

Molecules ◽  
2019 ◽  
Vol 24 (3) ◽  
pp. 572 ◽  
Author(s):  
Igor V. Komarov ◽  
Aleksandr Yu. Ishchenko ◽  
Aleksandr Hovtvianitsa ◽  
Viacheslav Stepanenko ◽  
Serhii Kharchenko ◽  
...  
Keyword(s):  
Proton Transfer ◽  
Model Compound ◽  
Bond Cleavage ◽  
Peptide Bond ◽  
Amide Bond ◽  
Carboxyl Group ◽  
Hydrolytic Cleavage ◽  
Sources Of Information ◽  
Peptide Bond Cleavage ◽  
Amide Bonds

Unconstrained amides that undergo fast hydrolysis under mild conditions are valuable sources of information about how amide bonds may be activated in enzymatic transformations. We report a compound possessing an unconstrained amide bond surrounded by an amino and a carboxyl group, each mounted in close proximity on a bicyclic scaffold. Fast amide hydrolysis of this model compound was found to depend on the presence of both the amino and carboxyl functions, and to involve a proton transfer in the rate-limiting step. Possible mechanisms for the hydrolytic cleavage and their relevance to peptide bond cleavage catalyzed by natural enzymes are discussed. Experimental observations suggest that the most probable mechanisms of the model compound hydrolysis might include a twisted amide intermediate and a rate-determining proton transfer.

Insight into nucleophilic fragmentation mechanisms by glutamic acid side chain in singly protonated glutathione and related peptidyl ions

2019 ◽  
Vol 26 (3) ◽  
pp. 175-186
Author(s):  
Liqun Fan ◽  
Jinhu Wang ◽  
Chunli Liu ◽  
Tiesheng Shi ◽  
Xian-Man Zhang ◽  
...  
Keyword(s):  
Oxygen Atom ◽  
Nucleophilic Addition ◽  
Theoretical Calculations ◽  
Bond Cleavage ◽  
Amide Bond ◽  
Side Chain ◽  
Carboxyl Oxygen Atom ◽  
Amide Bonds ◽  
Amide Bond Cleavage ◽  
Fragmentation Mechanisms

Fragmentation mechanisms of the singly protonated glutathione ( γ-ECG) and its synthetic analogue peptides (ECG and PPECG) have been investigated by liquid chromatography tandem-mass spectrometry and theoretical calculations. In the mass spectra, similar fragmentation patterns were observed for γ-ECG and ECG, but a completely different one was found in the case of PPECG. The E–C amide bond cleavage is the predominant pathway for the fragmentation of γ-ECG and ECG, whereas the additional N-terminal prolyl residues in PPECG significantly suppress the E–C amide bond cleavage. Theoretical calculations reveal that the fragmentation efficiencies of the E–C bonds in the protonated γ-ECG and ECG are much higher than that in the protonated PPECG, being attributed to their lower barriers of the potential energy; clearly the introduction of two prolyl residues can increase substantially the potential energy barrier. In the proposed mechanism, the protonated E–C amide bonds in the three peptides are first weakened followed by a nucleophilic addition by the glutamyl carboxyl oxygen atom in side chain, leading to the breaking of the E–C amide bonds. However, the processes of E–C bond fragmentation for three protonated analogs were not collaborative. Protonated amide bonds first fragment, then the nucleophilic addition by the side chain of glutamyl carboxyl oxygen atom takes places. On the other hand, the prolyl residues in PPECG can largely diminish the nucleophilic addition, resulting in a much lower efficiency of its E–C amide bond breaking. Distance analysis indicates that breaking the E–C amide bonds in the protonated γ-ECG, ECG, and PPECG ions could not occur without the assistance from the nucleophilic attack, highlighting an asynchronous collaborative process in the bond breakings.

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