The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Michal Szostak - One of the best experts on this subject based on the ideXlab platform.
-
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, Steven P. Nolan, Tongliang Zhou, Albert Poater, Luigi Cavallo, 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.
-
twisted n acyl hydantoins rotationally inverted urea imides of relevance in n c o cross coupling
Journal of Organic Chemistry, 2018Co-Authors: Roman Szostak, Roger A. Lalancette, Michal SzostakAbstract:We report a combined structural and computational study on the properties of twisted acyclic hydantoins. These compounds feature cyclic urea-imide moiety that is widely found in bioactive compounds and is structurally related to the classic bridged hydantoins proposed by Smissman more than 50 years ago. We demonstrate that C to N-substitution of the imide moiety in the succinimide ring to give hydantoin results in one of the most distorted acyclic Amide bonds reported to date. The energetic properties of twisted acyclic hydantoins with respect to structures, resonance energies, barriers to rotation, and proton affinities are discussed. The energetic and structural properties of twisted acyclic hydantoins described provide a benchmark to facilitate the development of twisted Amides based on the biorelevant cyclic urea-imide scaffold.
-
Structures of Highly Twisted Amides Relevant to Amide N−C Cross‐Coupling: Evidence for Ground‐State Amide Destabilization
Chemistry: A European Journal, 2016Co-Authors: Vittorio Pace, Guangrong Meng, Roger A. Lalancette, Roman Szostak, Wolfgang Holzer, Michal SzostakAbstract:Herein, we show that acyclic Amides that have recently enabled a series of elusive transition-metal-catalyzed N−C activation/cross-coupling reactions are highly twisted around the N−C(O) axis by a new destabilization mechanism of the Amide bond. A unique effect of the N-glutarimide substituent, leading to uniformly high twist (ca. 90°) irrespective of the steric effect at the carbon side of the Amide bond has been found. This represents the first example of a twisted Amide that does not bear significant steric hindrance at the α-carbon atom. The 15N NMR data show linear correlations between electron density at nitrogen and Amide bond twist. This study strongly supports the concept of Amide bond ground-state twist as a blueprint for activation of Amides toward N−C bond cleavage. The new mechanism offers considerable opportunities for organic synthesis and biological processes involving non-planar Amide bonds.
-
rhodium catalyzed c h bond functionalization with Amides by double c h c n bond activation
Organic Letters, 2016Co-Authors: Guangrong Meng, Michal SzostakAbstract:The first C–H bond functionalization with Amides as the coupling partners via selective activation of the Amide N–C bond using rhodium(I) catalysts under highly chemoselective conditions is reported. Notably, this report constitutes the first catalytic activation of the Amide N–C(O) bond by rhodium. We expect that this concept will have broad implications for using Amides as coupling partners for C–H activation beyond the work described herein.
-
general olefin synthesis by the palladium catalyzed heck reaction of Amides sterically controlled chemoselective n c activation
Angewandte Chemie, 2015Co-Authors: Guangrong Meng, Michal SzostakAbstract:Metal-catalyzed reactions of Amides proceeding via metal insertion into the NCO bond are severely underdeveloped due to resonance stabilization of the Amide bond. Herein we report the first Heck reaction of Amides proceeding via highly chemoselective NCO cleavage catalyzed by Pd0 utilizing Amide bond ground-state destabilization. Conceptually, this transformation provides access to a myriad of metal-catalyzed transformations of Amides via metal insertion/decarbonylation.
Subhash Chandra Ghosh - One of the best experts on this subject based on the ideXlab platform.
-
copper catalyzed oxidative amidation of aldehydes with amine salts synthesis of primary secondary and tertiary Amides
Journal of Organic Chemistry, 2012Co-Authors: Subhash Chandra Ghosh, Dang Thanh Tuan, Christina L. L. Chai, Joyce S Y Ngiam, Abdul Majeed Seayad, Anqi ChenAbstract:A practical method for the amidation of aldehydes with economic ammonium chloride or amine hydrochloride salts has been developed for the synthesis of a wide variety of Amides by using inexpensive copper sulfate or copper(I) oxide as a catalyst and aqueous tert-butyl hydroperoxide as an oxidant. This amidation reaction is operationally straightforward and provides primary, secondary, and tertiary Amides in good to excellent yields for most cases utilizing inexpensive and readily available reagents under mild conditions. In situ formation of amine salts from free amines extends the substrate scope of the reaction. Chiral Amides are also synthesized from their corresponding chiral amines without detectable racemization. The practicality of this Amide formation reaction has been demonstrated in an efficient synthesis of the antiarrhythmic drug N-acetylprocainAmide.
-
iron catalyzed efficient synthesis of Amides from aldehydes and amine hydrochloride salts
Advanced Synthesis & Catalysis, 2012Co-Authors: Subhash Chandra Ghosh, Christina L. L. Chai, Joyce S Y Ngiam, Abdul Majeed Seayad, Tuan Thanh Dang, Anqi ChenAbstract:A practical and efficient method for the synthesis of Amides has been developed by iron-cat- alysed oxidative amidation of aldehydes with amine hydrochloride salts. A wide range of Amides have been obtained in good to excellent yields under mild conditions. The application of this novel Amide formation reaction to the synthesis of pharmaceuti- cal compounds has been successfully demonstrated.
-
direct Amide synthesis from either alcohols or aldehydes with amines activity of ru ii hydride and ru 0 complexes
Journal of Organic Chemistry, 2010Co-Authors: Senthilkumar Muthaiah, Subhash Chandra Ghosh, Cheng Chen, Jian Zhang, Soon Hyeok HongAbstract:An in situ generated catalyst from readily available RuH2(PPh3)4, an N-heterocyclic carbene (NHC) precursor, NaH, and acetonitrile was developed. The catalyst showed high activity for the Amide synthesis directly from either alcohols or aldehydes with amines. When a mixture of an alcohol and an aldehyde was reacted with an amine, both of the corresponding Amides were obtained with good yields. Homogeneous Ru(0) complexes such as (η4-1,5-cyclooctadiene)(η6-1,3,5-cyclooctatriene)ruthenium [Ru(cod)(cot)] and Ru3(CO)12 were also active in the amidation of an alcohol or an aldehyde with the help of an in situ generated NHC ligand.
Anqi Chen - One of the best experts on this subject based on the ideXlab platform.
-
copper catalyzed oxidative amidation of aldehydes with amine salts synthesis of primary secondary and tertiary Amides
Journal of Organic Chemistry, 2012Co-Authors: Subhash Chandra Ghosh, Dang Thanh Tuan, Christina L. L. Chai, Joyce S Y Ngiam, Abdul Majeed Seayad, Anqi ChenAbstract:A practical method for the amidation of aldehydes with economic ammonium chloride or amine hydrochloride salts has been developed for the synthesis of a wide variety of Amides by using inexpensive copper sulfate or copper(I) oxide as a catalyst and aqueous tert-butyl hydroperoxide as an oxidant. This amidation reaction is operationally straightforward and provides primary, secondary, and tertiary Amides in good to excellent yields for most cases utilizing inexpensive and readily available reagents under mild conditions. In situ formation of amine salts from free amines extends the substrate scope of the reaction. Chiral Amides are also synthesized from their corresponding chiral amines without detectable racemization. The practicality of this Amide formation reaction has been demonstrated in an efficient synthesis of the antiarrhythmic drug N-acetylprocainAmide.
-
iron catalyzed efficient synthesis of Amides from aldehydes and amine hydrochloride salts
Advanced Synthesis & Catalysis, 2012Co-Authors: Subhash Chandra Ghosh, Christina L. L. Chai, Joyce S Y Ngiam, Abdul Majeed Seayad, Tuan Thanh Dang, Anqi ChenAbstract:A practical and efficient method for the synthesis of Amides has been developed by iron-cat- alysed oxidative amidation of aldehydes with amine hydrochloride salts. A wide range of Amides have been obtained in good to excellent yields under mild conditions. The application of this novel Amide formation reaction to the synthesis of pharmaceuti- cal compounds has been successfully demonstrated.
Makoto Fujita - One of the best experts on this subject based on the ideXlab platform.
-
Enhanced reactivity of twisted Amides inside a molecular cage
Nature Chemistry, 2020Co-Authors: Hiroki Takezawa, Kosuke Shitozawa, Makoto FujitaAbstract:When an Amide group is distorted from its planar conformation, the conjugation between the nitrogen lone pair and the π * orbital of the carbonyl is disrupted and the reactivity towards nucleophiles is enhanced. Although there are several reports on the synthesis of activated twisted Amides, Amide activation through mechanical twisting is much less common. Here, we report twisted Amides that are stabilized through their inclusion in a self-assembled coordination cage. When secondary aromatic Amides are included in a T _d-symmetric cage, the cis -twisted conformation is favoured over the trans -planar one—as evidenced by single-crystal X-ray diffraction analysis—revealing that the Amide can twist by up to 34°. As a consequence of this distortion, the hydrolysis of Amides is significantly accelerated upon inclusion. The distortion of an Amide group away from a planar conformation typically enhances its reactivity and such activation is usually achieved through the chemical synthesis of twisted Amides. Now, it has been shown that a non-covalent activation strategy leading to accelerated hydrolysis can be achieved by binding a reactive twisted Amide conformer inside a molecular cage.
Shannon S Stahl - One of the best experts on this subject based on the ideXlab platform.
-
discovery and mechanistic study of aliii catalyzed transamidation of tertiary Amides
Journal of the American Chemical Society, 2008Co-Authors: Justin M Hoerter, Karin M Otte, Samuel H. Gellman, Shannon S StahlAbstract:Cleavage of the C−N bond of carboxAmides generally requires harsh conditions. This study reveals that tris(amido)AlIII catalysts, such as Al2(NMe2)6, promote facile equilibrium-controlled transamidation of tertiary carboxAmides with secondary amines. The mechanism of these reactions was investigated by kinetic, spectroscopic, and density functional theory (DFT) computational methods. The catalyst resting state consists of an equilibrium mixture of a tris(amido)AlIII dimer and a monomeric tris(amido)AlIII−carboxAmide adduct, and the turnover-limiting step involves intramolecular nucleophilic attack of an amido ligand on the coordinated carboxAmide or subsequent rearrangement (intramolecular ligand substitution) of the tetrahedral intermediate. Fundamental mechanistic differences between these tertiary transamidation reactions and previously characterized transamidations involving secondary Amides and primary amines suggest that tertiary Amide/secondary amine systems are particularly promising for future de...
