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Introduction
Published in Andrew M. Harned, Nonnitrogenous Organocatalysis, 2017
A report from the MacMillan laboratory also appeared in 2000 concerning asymmetric Diels–Alder reactions that were catalyzed by a phenyl alanine-derived imidazolidinone catalyst.14 This initial report was quickly followed by reports of other asymmetric cycloaddtions,15 Friedel–Crafts alkylations,16 and Mukaiyama–Michael reactions (Figure 1.4).17 All of these reactions are predicated on the formation of an iminium ion (8) from the α,β-unsaturated aldehyde starting material and the imidazolidinone catalyst. Once formed, the iminium ion would have a lowest unoccupied molecular orbital (LUMO)-lowering effect similar to that of a Lewis acid–aldehyde complex. This activation manifold has come to be called iminium ion catalysis and, much like the proline-catalyzed reactions earlier, has proven to be applicable to numerous reaction types.13 The orthogonal reactivity of the nucleophilic enamines and electrophilic iminium ions can even work in concert, thus allowing one to devise powerful cascade reactions.18
Diversity-Oriented Synthesis of Substituted and Fused β-Carbolines from 1-Formyl-9H-β-Carboline Scaffolds
Published in Tanmoy Chakraborty, Lalita Ledwani, Research Methodology in Chemical Sciences, 2017
Nisha Devi, Ravindra K. Rawal, Virender Singh
Mechanistically, it was proposed that initially secondary amines reacted with the aldehyde (51) leading to the formation of iminium ion with the loss of a water molecule (Fig. 5.9). Subsequently, Cu-coordinated alkyne formed in situ reacted with imine, wherein a nucleophilic attack of pyridyl nitrogen (N-2) on the Cu-coordinated allenyl double bond occurs, resulting in the formation of cationic intermediate (60). Thereafter, the secondary amine captures a proton from 60 to furnish the intermediate, 61, which upon deprotonation yielded the 3-aminoindolizino[8,7-b]indoles derivatives (59).
Symbols, Terminology, and Nomenclature
Published in W. M. Haynes, David R. Lide, Thomas J. Bruno, CRC Handbook of Chemistry and Physics, 2016
W. M. Haynes, David R. Lide, Thomas J. Bruno
Quadrupole moment - A coefficient of the third term (after monopole and dipole) in the power series expansion of the electric potential of an array of charges. A nucleus of spin greater than 1/2 has a non-vanishing nuclear quadrupole moment which can interact with the electric field gradient of the surrounding electrons. Molecular quadrupole moments have an influence on intermolecular forces. Quality factor (Q) - The ratio of the absolute value of the reactance of an electrical system to the resistance; thus a measure of the energy stored per cycle relative to the energy dissipated. Quantum yield - In photochemistry, the number of moles transformed in a specific process, either physically (e.g., by emission of photons) or chemically, per mole of photons absorbed by the system. [3] Quark - An elementary entity which has not been directly observed but is considered a constituent of protons, neutrons, and other hadrons. Quasar - An extragalactic object emitting electromagnetic radiation at a very high power level and showing a very large red shift, thus indicating that the object is receding at a speed approaching the speed of light. Quasicrystal - A solid having conventional crystalline properties but whose lattice does not display translational periodicity. Quaternary ammonium compounds - Derivatives of ammonium compounds, NH4+ Y-, in which all four of the hydrogens bonded to nitrogen have been replaced with hydrocarbyl groups. Compounds having a carbon-nitrogen double bond (i.e. R2C=N+R2Y-) are more accurately called iminium compounds. [5] Quinones - Compounds having a fully conjugated cyclic dione structure, such as that of benzoquinones, derived from aromatic compounds by conversion of an even number of -CH= groups into -C(=O)- groups with any necessary rearrangement of double bonds. [5] Racemic mixture - A mixture of equal amounts of a pair of enantiomers (optical isomers); such a mixture is not optically active. Rad - A non-SI unit of absorbed dose of radiation, equal to 0.01 Gy. Radiance (L) - The radiant intensity in a given direction from an element of a surface, divided by the area of the orthogonal projection of this element on a plane perpendicular to the given direction. [1] Radiant intensity (I) - The radiant energy flux leaving an element of a source within an element of solid angle, divided by that element of solid angle. [1] Radicals - Molecular entities possessing an unpaired electron, such as CH3, SnH3, Cl. (In these formulas the dot, symbolizing the unpaired electron, should be placed so as to indicate the atom of highest spin density, if this is possible). [5] Raman effect - The inelastic scattering of light by a molecule, in which the incident photon either gives up to, or receives energy from, one of the internal vibrational modes of the molecule. The scattered light thus has either a lower frequency (Stokes radiation) or higher frequency (anti-Stokes radiation) than the incident light. These shifts provide a measure of the normal vibrational frequencies of the molecule. Rankine cycle - A thermodynamic cycle which can be used to calculate the ideal performance of a heat engine that uses a condensable vapor as the working fluid (e.g., a steam engine or a heat pump).
γ-aminobutyric acid and collagen peptides as recyclable bifunctional biocatalysts for the solvent-free one-pot synthesis of 2-aminobenzothiazolomethyl-2-naphthols
Published in Green Chemistry Letters and Reviews, 2018
Maryam Fardpour, Ali Safari, Shahrzad Javanshir
Based on the above results and the previous reports, plausible mechanisms for these two methods are given in Schemes 2 and 3. The reaction mechanism for method A starts with the nucleophilic addition of the amine group of amino acid to the carbonyl group of aldehyde followed by dehydration which leads to the formation of iminium ion A that undergoes reaction with 2-naphtol to give the Mannich base B. Intermediate B is in equilibrium with its zwitterion form C that undergoes amino acid elimination to form the ortho-quinone methide D. Finally, o-QM D readily reacts with 2-aminobenzothiazole to produce the desired product 5 and GABA goes back to the catalytic cycle as an active catalyst (Scheme 2). The proposed mechanism for method B is depicted in Scheme 3.
Mixed bases mediated synthesis of thioamides in water
Published in Journal of Sulfur Chemistry, 2020
Jiao Li, Xuanhe Ren, Ganzhong Li, Helong Liang, Yajie Zhao, Zhiwu Wang, Heng Li, Bingxin Yuan
Based on previous reports [27,38,39], and our experimental results, the plausible reaction mechanism is proposed in Scheme 1. Initially, amine is formed by decarbonylation of formamide and undergoes nucleophilic attack to an aryl aldehyde, generating the iminium intermediate A. In the meantime, elemental sulfur undergoes nucleophilic attack by amine to form polysulfide B. Then, the iminium A react with polysulfide B to afford intermediate C. In the final step, elemental-sulfur-promoted oxidation of intermediate C releases the target product.