Experimental and Computational Mechanistic Studies of the β-Diketiminatoiron(II)-Catalysed Hydroamination of Primary Aminoalkenes

A comprehensive mechanistic study by means of complementary experimental and computational approaches of the exo-cyclohydroamination of primary aminoalkenes mediated by the recently reported β-diketiminatoiron(II) complex B is presented. Kinetic analysis of the cyclisation of 2,2-diphenylpent-4-en-1-amine ( 1 a ) catalysed by B revealed a first-order dependence of the rate on both aminoalkene and catalyst concentrations and a primary kinetic isotope effect (KIE) (k_H/k_D) of 2.7 (90 °C). Eyring analysis afforded ΔH^≠=22.2 kcal mol⁻¹, ΔS^≠=−13.4 cal mol⁻¹ K⁻¹. Plausible mechanistic pathways for competitive avenues of direct intramolecular hydroamination and oxidative amination have been scrutinised computationally. A kinetically challenging proton-assisted concerted N−C/C−H bond-forming non-insertive pathway is seen not to be accessible in the presence of a distinctly faster σ-insertive pathway. This operative pathway involves 1) rapid and reversible syn-migratory 1,2-insertion of the alkene into the Fe−N_amido σ bond at the monomer {N^N}Fe^II amido compound; 2) turnover-limiting Fe−C σ bond aminolysis at the thus generated transient {N^N}Fe^II alkyl intermediate and 3) regeneration of the catalytically competent {N^N}Fe^II amido complex, which favours its dimer, likely representing the catalyst resting state, through rapid cycloamine displacement by substrate. The collectively derived mechanistic picture is consonant with all empirical data obtained from stoichiometric, catalytic and kinetics experiments.     

Studies of Nucleophilic Substitution Reactions of p‐Nitrophenyl Acetate with Some Dihydroxamate Ions in Cationic Micellar Media

Pseudo‐first‐order rate constants have been determined for the nucleophilic substitution reactions of p‐nitrophenyl acetate with oxalo, malono, and succinodihydroxamate ions (^?ONHC(O)(CH₂)_nC(O)NHO^?) in phosphate buffer (pH=7.9) at 27°C. The rate data of the reaction revealed that the nucleophilic reactivity sequence of these hydroxamate ions is generally ODHA>MDHA>SDHA. The k_obs value increases upon addition of cationic surfactants to the reaction medium which is typical behavior of micelle‐assisted bimolecular reactions. The pseudo‐phase ion exchange model has been successfully applied to determine binding constant.     

Studies of Birch Reductive Alkylation of Substituted α-Tetralones

A series of α-tetralones, with different degree of substitution, was submitted to the Birch reduction-alkylation procedure using various alkylating agents, to produce angularly substituted 1,4-unsaturated decalones. The stereoselectivity behavior of such dienones upon reduction is also described.     

Intramolecular Oxonium-Ene Reaction: Scope and Mechanistic Studies

Substituted tetrahydrofurans are widely used as synthetic intermediates and they are also featured widely in natural products. Among the many methods available for the synthesis of this class of compounds, intramolecular-ene reaction is one of the most attractive methods. Recently, Lob group has established a convergent approach to various cyclic ethers via an intramolecular (3,5)-oxonium-ene type cyclizations.[1,2] We employed E-homoallylic alcohols with aldehydes using indium triflate as a catalyst to study intramolecular (3,5)-oxonium-ene type cyclizations, with the yields ranging from 37% to 95% and the selectivities de from 60 : 40 to 99; 1.     

Thiaporphyrin with an Inverted Thiophene Ring – DFT Studies

The structure and electronic energy have been investigated applyingthe density functional theory (DFT) for two idealized 2-thia-21-carbaporphyrin, (SCP)H and (3H-SCP), 2-thia-21-carbaporphyrin anion (SCP)^- and 21-thiaporphyrin (SP)H. The analysis of calculated total electronic energies, using the B3LYP/6-31-G^* approach, demonstrates that the energy difference between 21-thiaporphyrin and its inverted isomer equals 10.34 kcal/mol [(SCP)H] and 52.08 kcal/mol [(3H-SCP)]. In contrast to 21-thiaporphyrin thethiophene fragments in (SCP)H and SCP^- present a geometry resembling that one of an isolated thiophene molecule.     

A Multiple Hammett Study of the Nucleophilic Substitution Reaction of ∝-Carbonyl Derivatives

The reaction mechanism for the nucleophilic substitution reaction of substituted phenacyl benzenesulfonates with substituted pyridines in acetonitrile have been investigated by means of multiple Hammett correlation.     

Kinetic Studies on Ligand Substitution Reactions of Metallothioneins with DTPA and EDTA

Cd, Zn-thionelns were isolated from the rat liver by improved Winge method and purified further. The composition was determined. The mobilization of Cd ions from the Cd, Zn-metallothioneins was studied with spectrophotometric method. The results show that the reaction of DTP A or EDTA with Cd, Zn-thioneins occurs through three steps. The first step follows pseudo-first order reaction with association mechanism. The formation constants and the dissociation rate constants of the relevant intermediate ternary complexes and apparent rate constants, Kapp were determined. The properties and structure of Cd, Zn-thioneins and ligands with low molecular weights affect the values of Kapp.     

Introduction of N‐Containing Heterocycles into Pyrazole by Nucleophilic Aromatic Substitution

Abstract

The nucleophilic aromatic substitution on 5‐chloropyrazoles activated by the electron‐withdrawing formyl group offers a useful method to introduce a wide range of N‐containing heterocycles into them. The rate of reaction was greatly affected by the electronic nature of the N‐1 substitution.     

Metal Ion Promoted Nucleophilic Substitution of Hydrogen in Chelated Macrocyclic α-Di-Imine

Abstract

Base-catalyzed addition of nitromethane to the Ni(II) co-ordinated α-di-imine, followed by elimination of HNO₂ and rearrangement of the double bond formed, leads to the methyl substituted product, i.e. the nucleophilic substitution of the imine hydrogens occurred.     

Experimental (X-ray Diffraction,UV–Vis Spectroscopy) and DFT Studies of 1-Ethyl-3-methylquinoxaline-2-thione

Russian Journal of Physical Chemistry A - In this paper, we present the experimental and theoretical investigation of 1-ethyl-3-methylquinoxaline-2-thione, molecule exhibiting an important...     

Studies on Electrophilic Substitution of Quasi-Aromatic Metal Ion Complexes

The electrophilic substitution reaction occurring to the chelate ring of the complexes could be regarded as an indication of quasi-aromaticity of the ring systems, no catalyst was used and only triethylamine was employed, implying that the aroylating agents with different p-substituents are polarized enough to be effective electrophiles to attack the methine carbon of the electron-rich substrate 1. This property is probably the clue to polarization of the ligand electrons by the nickel( Ⅱ ) ion and to the participation of the nickel( Ⅱ ) in the π-bond systems of the two coordinated conjugated rings. The linearity relationship between vd-d maxima, E1/2OX(1) and σp are obtained, respectively. The electronic environment of central metal ion as well as the aromaticity of the ring system are affected by the electronic properties of the p-substituents. A comparison of the electrochemical results with each other showed .that when the electronegativity of the substituent was higher, the oxidation(Ni2+/Ni3+)     

The Mechanism of Acid-Catalyzed Nucleophilic Substitution in Decahydro-closo-Decaborate(2–) Anions

The reactions of salts formed by the B₁₀H^2– ₁₀anion with carboxylic acids were studied. From the model systems Cat₂B₁₀H₁₀+ HCOOH (Cat = Et₄N⁺, Bu₄N⁺, Ph₄P⁺, Ph₄As⁺), several intermediates were isolated and characterized. A mechanism was proposed for the replacement of the exo-polyhedral hydrogen atoms in B₁₀H^2– ₁₀by carboxylate groups in the reactions of Cat₂B₁₀H₁₀with carboxylic acids.     

Nucleophilic Displacements in Alkylphosphonates: P–O Versus P–C Bond Cleavage. A Combined DFT and Experimental Study

Abstract

Potential energy surfaces for the nucleophilic displacements at phosphorus in dimethyl methyl, chloromethyl, dichloromethyl, and trichloromethyl phosphonates have been computed by DFT methods. The results reveal that sequential introduction of chlorine substituents at the methyl group in methyl phosphonates increases the stability of transition states and intermediates, which facilitates P–C bond cleavage. While nonsubstituted dimethyl methylphosphonate may undergo exclusive P–O bond cleavage, the trichlorinated analogue reacts exclusively via P–C bond dissociation to form dichlorocarbene, which was trapped by various olefins to form the corresponding gem-dichlorocyclopropanes.     

Cyclopalladation and Reactivity of Amino Esters through C?H Bond Activation: Experimental,Kinetic, and Density Functional Theory Mechanistic Studies

The orthopalladation, through C? H bond activation, of a large number of amino esters and amino phosphonates derived from phenylglycine, and having different substituents at the aryl ring and the C‐α atom, as well as on the N‐amine atom, has been studied. The experimental observations indicated an improvement in the yields of the orthopalladated compounds when the N‐amine and/or the C‐α atom are substituted, when compared with the unsubstituted methyl phenylglycinate derivatives. In contrast, substitutions at the aryl ring do not promote significant changes in the orthometalation results. Furthermore, the use of hydrochloride salts of the amino esters has also been shown to have a remarkably favorable effect on the process. All these observations have been fully quantified at different temperatures and pressures by a detailed kinetic study in solution in different solvents and in the presence and absence of added Brønsted acids and chloride anions. The data collected indicate relevant changes in the process depending on these conditions, as expected from the general background known for cyclopalladation reactions. An electronic mechanism of the orthopalladation has been proposed based on DFT calculations at the B3LYP level, and a very good agreement between the trends kinetically measured and the theoretically calculated activation barriers has been obtained. The reactivity of the new orthopalladated amino phosphonate derivatives has been tested and it was found that their halogenation, alkoxylation and carbonylation resulted in formation of the corresponding functionalized ortho‐haloaminophosphonates, ortho‐alkoxyaminophosphonates and oxoisoindolinylphosphonates.     

Nucleophilic Substitution Reaction of p-Dinitrobenzene by a Carbanion: Evidence for Electron Transfer Mechanism

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Nucleophilic Vinylic Substitution in Perfluoroacylchromenes. Diastereoselective Synthesis of Push–Pull Enamino Ketones

Russian Journal of Organic Chemistry - The reactions of 2-perfluoroacyl-1H-benzo[f]chromenes and 6,7-dimethyl-3-trifluoroacetyl-4H-chromene with primary aliphatic amines and ammonia afforded a...