The Experts below are selected from a list of 2370 Experts worldwide ranked by ideXlab platform
Michal Szostak - One of the best experts on this subject based on the ideXlab platform.
-
non classical amide bond formation Transamidation and amidation of activated amides and esters by selective n c o c cleavage
Synthesis, 2020Co-Authors: Guangchen Li, Michal SzostakAbstract: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 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
-
Non-Classical Amide Bond Formation: Transamidation and Amidation of Activated Amides and Esters by Selective N–C/O–C Cleavage
Synthesis, 2020Co-Authors: Michal Szostak, Guangchen LiAbstract: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
-
buchwald hartwig cross coupling of amides Transamidation by selective n c o cleavage mediated by air and moisture stable pd nhc allyl cl precatalysts catalyst evaluation and mechanism
Catalysis Science & Technology, 2020Co-Authors: Guangchen Li, Tongliang Zhou, Albert Poater, Luigi Cavallo, Steven P Nolan, Michal SzostakAbstract:The Pd–NHC-catalyzed acyl-type Buchwald–Hartwig cross-coupling of amides by N–C(O) cleavage (Transamidation) provides a valuable alternative to the classical methods for amide synthesis. Herein, we report a combined experimental and computational study of the Buchwald–Hartwig cross-coupling of amides using well-defined, air- and moisture-stable [Pd(NHC)(allyl)Cl] precatalysts. Most crucially, we present a comprehensive evaluation of a series of distinct Pd(II)–NHC precatalysts featuring different NHC scaffolds and throw-away ligands for the synthesis of functionalized amides that are not compatible with stoichiometric transition-metal-free Transamidation methods. Furthermore, we present evaluation of the catalytic cycle by DFT methods for a series of different Pd(II)–NHC precatalysts. The viability of accessing NHC-supported acyl-palladium(II) amido complexes will have implications for the design and development of cross-coupling methods involving stable amide electrophiles.
-
metal free Transamidation of secondary amides by n c cleavage
Journal of Organic Chemistry, 2019Co-Authors: Md Mahbubur Rahman, Guangchen Li, Michal SzostakAbstract:Transamidation reactions represent a fundamental chemical process involving conversion of one amide functional group into another. Herein, we report a facile, highly chemoselective method for Transamidation of N-tert-butoxycarbonylation (N-Boc) activated secondary amides that proceeds under exceedingly mild conditions in the absence of any additives. Because this reaction is performed in the absence of metals, oxidants, or reductants, the reaction tolerates a large number of useful functionalities. The reaction is compatible with diverse amides and nucleophilic amines, affording the Transamidation products in excellent yields through direct nucleophilic addition to the amide bond. The utility of this methodology is highlighted in the synthesis of Tigan, a commercial antiemetic, directly from the amide bond. We expect that this new metal-free Transamidation will have broad implications for the development of new transformations involving direct nucleophilic addition to the amide bond as a key step.
-
highly chemoselective transition metal free Transamidation of unactivated amides and direct amidation of alkyl esters by n c o c cleavage
Journal of the American Chemical Society, 2019Co-Authors: Guangchen Li, Michal Szostak, Chonglei Ji, Xin HongAbstract:The amide bond is one of the most fundamental functional groups in chemistry and biology and plays a central role in numerous processes harnessed to streamline the synthesis of key pharmaceutical and industrial molecules. Although the synthesis of amides is one of the most frequently performed reactions by academic and industrial scientists, the direct Transamidation of tertiary amides is challenging due to unfavorable kinetic and thermodynamic contributions of the process. Herein, we report the first general, mild, and highly chemoselective method for Transamidation of unactivated tertiary amides by a direct acyl N–C bond cleavage with non-nucleophilic amines. This operationally simple method is performed in the absence of transition metals and operates under unusually mild reaction conditions. In this context, we further describe the direct amidation of abundant alkyl esters to afford amide bonds with exquisite selectivity by acyl C–O bond cleavage. The utility of this process is showcased by a broad sc...
Sk Rasheed - One of the best experts on this subject based on the ideXlab platform.
-
Sulphuric acid immobilized on silica gel (H2SO4–SiO2) as an eco-friendly catalyst for Transamidation
RSC Advances, 2020Co-Authors: Sk Rasheed, A. Siva Reddy, Ravi ShankarAbstract:A novel method of Transamidation of carboxamides with amines by using catalytic amounts of H2SO4–SiO2 has been developed under solvent free conditions. The Transamidation is compatible with a wide range of aromatic, heteroaromatic, aliphatic, cyclic/acyclic primary or secondary amines. The metal/solvent-free conditions represent a significant improvement over other existing methods as the reaction can be performed in open air conditions and no column purification is required. The versatility of this methodology was further demonstrated by synthesizing the commercially available drug procainamide.
-
Sulfuric Acid Immobilized on Silica Gel (H2SO4—SiO2) as an Eco‐Friendly Catalyst for Transamidation.
ChemInform, 2015Co-Authors: Sk Rasheed, A. Siva Reddy, Ravi ShankarAbstract:Transamidation of a series of N,N-dimethyl amides with a wide range of primary and secondary amines is accomplished environmentally friendly using sulfuric acid adsorbed on silica gel as recyclable catalytic system.
-
sulfuric acid immobilized on silica gel h2so4 sio2 as an eco friendly catalyst for Transamidation
ChemInform, 2015Co-Authors: Sk Rasheed, Siva A Reddy, Ravi ShankarAbstract:Transamidation of a series of N,N-dimethyl amides with a wide range of primary and secondary amines is accomplished environmentally friendly using sulfuric acid adsorbed on silica gel as recyclable catalytic system.
-
sulphuric acid immobilized on silica gel h2so4 sio2 as an eco friendly catalyst for Transamidation
RSC Advances, 2015Co-Authors: Sk Rasheed, Siva A Reddy, Ravi ShankarAbstract:A novel method of Transamidation of carboxamides with amines by using catalytic amounts of H2SO4–SiO2 has been developed under solvent free conditions. The Transamidation is compatible with a wide range of aromatic, heteroaromatic, aliphatic, cyclic/acyclic primary or secondary amines. The metal/solvent-free conditions represent a significant improvement over other existing methods as the reaction can be performed in open air conditions and no column purification is required. The versatility of this methodology was further demonstrated by synthesizing the commercially available drug procainamide.
Guangchen Li - One of the best experts on this subject based on the ideXlab platform.
-
non classical amide bond formation Transamidation and amidation of activated amides and esters by selective n c o c cleavage
Synthesis, 2020Co-Authors: Guangchen Li, Michal SzostakAbstract: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 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
-
Non-Classical Amide Bond Formation: Transamidation and Amidation of Activated Amides and Esters by Selective N–C/O–C Cleavage
Synthesis, 2020Co-Authors: Michal Szostak, Guangchen LiAbstract: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
-
buchwald hartwig cross coupling of amides Transamidation by selective n c o cleavage mediated by air and moisture stable pd nhc allyl cl precatalysts catalyst evaluation and mechanism
Catalysis Science & Technology, 2020Co-Authors: Guangchen Li, Tongliang Zhou, Albert Poater, Luigi Cavallo, Steven P Nolan, Michal SzostakAbstract:The Pd–NHC-catalyzed acyl-type Buchwald–Hartwig cross-coupling of amides by N–C(O) cleavage (Transamidation) provides a valuable alternative to the classical methods for amide synthesis. Herein, we report a combined experimental and computational study of the Buchwald–Hartwig cross-coupling of amides using well-defined, air- and moisture-stable [Pd(NHC)(allyl)Cl] precatalysts. Most crucially, we present a comprehensive evaluation of a series of distinct Pd(II)–NHC precatalysts featuring different NHC scaffolds and throw-away ligands for the synthesis of functionalized amides that are not compatible with stoichiometric transition-metal-free Transamidation methods. Furthermore, we present evaluation of the catalytic cycle by DFT methods for a series of different Pd(II)–NHC precatalysts. The viability of accessing NHC-supported acyl-palladium(II) amido complexes will have implications for the design and development of cross-coupling methods involving stable amide electrophiles.
-
metal free Transamidation of secondary amides by n c cleavage
Journal of Organic Chemistry, 2019Co-Authors: Md Mahbubur Rahman, Guangchen Li, Michal SzostakAbstract:Transamidation reactions represent a fundamental chemical process involving conversion of one amide functional group into another. Herein, we report a facile, highly chemoselective method for Transamidation of N-tert-butoxycarbonylation (N-Boc) activated secondary amides that proceeds under exceedingly mild conditions in the absence of any additives. Because this reaction is performed in the absence of metals, oxidants, or reductants, the reaction tolerates a large number of useful functionalities. The reaction is compatible with diverse amides and nucleophilic amines, affording the Transamidation products in excellent yields through direct nucleophilic addition to the amide bond. The utility of this methodology is highlighted in the synthesis of Tigan, a commercial antiemetic, directly from the amide bond. We expect that this new metal-free Transamidation will have broad implications for the development of new transformations involving direct nucleophilic addition to the amide bond as a key step.
-
highly chemoselective transition metal free Transamidation of unactivated amides and direct amidation of alkyl esters by n c o c cleavage
Journal of the American Chemical Society, 2019Co-Authors: Guangchen Li, Michal Szostak, Chonglei Ji, Xin HongAbstract:The amide bond is one of the most fundamental functional groups in chemistry and biology and plays a central role in numerous processes harnessed to streamline the synthesis of key pharmaceutical and industrial molecules. Although the synthesis of amides is one of the most frequently performed reactions by academic and industrial scientists, the direct Transamidation of tertiary amides is challenging due to unfavorable kinetic and thermodynamic contributions of the process. Herein, we report the first general, mild, and highly chemoselective method for Transamidation of unactivated tertiary amides by a direct acyl N–C bond cleavage with non-nucleophilic amines. This operationally simple method is performed in the absence of transition metals and operates under unusually mild reaction conditions. In this context, we further describe the direct amidation of abundant alkyl esters to afford amide bonds with exquisite selectivity by acyl C–O bond cleavage. The utility of this process is showcased by a broad sc...
Ravi Shankar - One of the best experts on this subject based on the ideXlab platform.
-
Sulphuric acid immobilized on silica gel (H2SO4–SiO2) as an eco-friendly catalyst for Transamidation
RSC Advances, 2020Co-Authors: Sk Rasheed, A. Siva Reddy, Ravi ShankarAbstract:A novel method of Transamidation of carboxamides with amines by using catalytic amounts of H2SO4–SiO2 has been developed under solvent free conditions. The Transamidation is compatible with a wide range of aromatic, heteroaromatic, aliphatic, cyclic/acyclic primary or secondary amines. The metal/solvent-free conditions represent a significant improvement over other existing methods as the reaction can be performed in open air conditions and no column purification is required. The versatility of this methodology was further demonstrated by synthesizing the commercially available drug procainamide.
-
Sulfuric Acid Immobilized on Silica Gel (H2SO4—SiO2) as an Eco‐Friendly Catalyst for Transamidation.
ChemInform, 2015Co-Authors: Sk Rasheed, A. Siva Reddy, Ravi ShankarAbstract:Transamidation of a series of N,N-dimethyl amides with a wide range of primary and secondary amines is accomplished environmentally friendly using sulfuric acid adsorbed on silica gel as recyclable catalytic system.
-
sulfuric acid immobilized on silica gel h2so4 sio2 as an eco friendly catalyst for Transamidation
ChemInform, 2015Co-Authors: Sk Rasheed, Siva A Reddy, Ravi ShankarAbstract:Transamidation of a series of N,N-dimethyl amides with a wide range of primary and secondary amines is accomplished environmentally friendly using sulfuric acid adsorbed on silica gel as recyclable catalytic system.
-
sulphuric acid immobilized on silica gel h2so4 sio2 as an eco friendly catalyst for Transamidation
RSC Advances, 2015Co-Authors: Sk Rasheed, Siva A Reddy, Ravi ShankarAbstract:A novel method of Transamidation of carboxamides with amines by using catalytic amounts of H2SO4–SiO2 has been developed under solvent free conditions. The Transamidation is compatible with a wide range of aromatic, heteroaromatic, aliphatic, cyclic/acyclic primary or secondary amines. The metal/solvent-free conditions represent a significant improvement over other existing methods as the reaction can be performed in open air conditions and no column purification is required. The versatility of this methodology was further demonstrated by synthesizing the commercially available drug procainamide.
Subbarayappa Adimurthy - One of the best experts on this subject based on the ideXlab platform.
-
h β zeolite catalyzed Transamidation of carboxamides phthalimide formamides and thioamides with amines under neat conditions
ChemInform, 2016Co-Authors: Darapaneni Chandra Mohan, Subbarayappa AdimurthyAbstract:A green method for the Transamidation and thioamidation using H-β-zeolite as heterogeneous recyclable catalyst is developed.
-
h β zeolite catalyzed Transamidation of carboxamides phthalimide formamides and thioamides with amines under neat conditions
RSC Advances, 2015Co-Authors: Darapaneni Chandra Mohan, Subbarayappa AdimurthyAbstract:Efficient Transamidation of unactivated carboxamides, phthalimides, formamides and thioamides with amines under solvent-free conditions using H-β-zeolite as a green and recyclable heterogeneous catalyst is described. Easy work up, high purity of the products, recyclability and environmentally-friendly nature of the catalyst are the attractive features of the present methodology. This is the first report for the Transamidation of thioamides under heterogeneous conditions.
-
chitosan an efficient recyclable catalyst for Transamidation of carboxamides with amines under neat conditions
ChemInform, 2015Co-Authors: Darapaneni Chandra Mohan, Subbarayappa AdimurthyAbstract:A series of amide derivatives (I) and (IV) as well as more challenging aryl and alkyl amines (VII) with long-chain alkyl substituents are selectively converted into the corresponding Transamidation products (III), (VI) and (IX), which are frequently found in biologically active compounds.
-
chitosan an efficient recyclable catalyst for Transamidation of carboxamides with amines under neat conditions
Green Chemistry, 2014Co-Authors: Darapaneni Chandra Mohan, Subbarayappa AdimurthyAbstract:A novel chitosan-catalyzed Transamidation of carboxamides with amines under solvent-free conditions is described. A series of amide derivatives as well as more challenging aryl and alkyl amines with long-chain alkyl substituents could be selectively converted into the corresponding Transamidation products, which are frequently found in biologically active compounds and pharmaceuticals. Under similar reaction conditions benzo[d]heterocycles were also obtained via a one-pot synthesis through Transamidation and subsequent dehydration. Recyclability of chitosan was demonstrated, with quantitative yields of products obtained without any loss of catalytic activity.
-
l proline an efficient catalyst for Transamidation of carboxamides with amines
ChemInform, 2013Co-Authors: Darapaneni Chandra Mohan, Subbarayappa AdimurthyAbstract:The Transamidation of carboxamides is achieved under solvent-free conditions providing a wide range of aliphatic, propargylic, benzylic, aromatic, and heteroaromatic Transamidation products in moderate to high yields.
