Isomerization Of Imines Research Articles

Z/E(C=C)-isomerization and fluorescence modulation of imines of 7-N,N-dialkylamino-4-hydroxy-3-formylcoumarins in organic solvents

<i>Z/E</i>(C=C)-isomerization and fluorescence modulation of imines of 7-<i>N,N</i>-dialkylamino-4-hydroxy-3-formylcoumarins in organic solvents

Z/E (C=C)-isomerization and fluorescence modulation of imines of 7-N,N-dialkylamino-4-hydroxy-3-formylcoumarins in organic solvents

Imines of 7-dialkylamino-3-formyl-4-hydroxycoumarins have been found to exist in Z-ketoenamine form in crystal state and undergo Z/E-isomerization around C=C bond in organic solvents at room temperature. Activation energies of isomerization have been measured experimentally and calculated by the DFT B3LYP method. Transition of ketoenamine form of p-nitrophenylimines into (hydroxy)imine form at low concentration (10-5 m) in polar solvents is accompanied by strong increase in fluorescence.

Pyrimidine based highly sensitive fluorescent receptor for Al3+ showing dual signalling mechanism

A new fluorescent probe (5-[(4-diethylamino-2-hydroxy-benzylidene)-amino]-1H-pyrimidine-2, 4-dione) (Receptor 1) has been synthesized by the Schiff base condensation of 5-aminouracil with 4-(diethylamino)salicylaldehyde. The receptor 1 exhibits high selectively for Al(3+) in DMSO as well as in aqueous solution even in the presence of biologically relevant cations such as Na(+), K(+), Ca(2+), Mg(2+), Pb(2+) and several transition metal ions. The lowest detection limit for the receptor 1 was found to be 1.62 × 10(-10) M with its linear response towards Al(3+) in the concentration range of 1.75 × 10(-9) to 3.3 × 10(-8) M in DMSO. Receptor 1 is the first ever example where a single molecular probe is able to show imine (C=N) isomerization inhibition along with twisted intramolecular charge transfer (TICT) in combinatorial fashion.

Solvent-induced E/Z(C=N)-isomerization of imines of some hydroxy-substituted formylcoumarins

Aromatic imines, namely, 5-formyl-6-hydroxy-4-methyl- and 8-formyl-7-hydroxy-4-methylcoumarin derivatives, have been synthesized. A dependence of their spectral characteristics (1H NMR spectra, electronic absorption spectra) from the solvent (DMSO, CHCl3, DMF, acetonitrile, MeOH) has been studied. The solvatochromic effects observed for a number of imines, first of all, for 7-hydroxy-4-methyl-8-(4′-nitrophenylimino)methyl-2H-1-benzopyran-2-one, were related to their E/Z-isomerization with respect to the C=N bond based on the quantum chemical calculations by the AM1, PM3, PPP CI methods.

Post‐Schiff Base Chemistry of the Maillard Reaction

Schiff bases play a critical role, not only in initiating the Maillard reaction, but also in its propagation. Little attention has been paid so far to the ability of these imines to undergo isomerization and thus contribute to the diversity of Maillard reaction products. In this study, imine isomerization through 5-oxazolidinone formation was explored in a phenylalanine/glyceraldehyde model system, and spectroscopic evidence was provided for its formation by taking advantage of the strong carbonyl absorption band centered at 1784 cm(-1). The importance of 5-oxazolidinone formation lies in its ability to decarboxylate to azomethine ylide and subsequently form two isomeric imines, each capable of producing distinct Maillard products. Evidence for the formation of such ylides was also provided through their ability to undergo 1,3-dipolar cycloaddition with dipolarophiles.

Kinetics and mechanism of triethylamine-catalyzed 1,3-proton shift: Optimized and substantially improved reaction conditions for biomimetic reductive amination of fluorine-containing carbonyl compounds

Kinetic study of the triethylamine (TEA)-catalyzed isomerization of imine, derived from benzylamine and trifluoroacetophenone to the corresponding N-benzylidene-2,2,2-trifluoro-1-(phenyl)ethylamine has revealed concerted nature of the mechanism of this reaction via a virtually unionized transition state. As a synthetic bonus of this kinetic study, we found that application of a polar solvent (acetonitrile) and four equivalents of TEA provide for optimal reaction conditions at high concentrations. We demonstrate that application of these reaction conditions allows to substantially increase the reaction rates, chemical yields and results in cleaner formation of the target products.

Isomerization of an imine intermediate in a reductive amination reaction over metal catalysts

The reductive amination reaction of acetone by cyclohexylamine over hydrogenation metal catalysts was investigated. The study is focused on the formation of side products in the reaction. It was verified that the formation of amines having unusual combinations of alkyls is caused by the metal-catalyzed rearrangement of the double bond around the nitrogen atom in an imine intermediate and consequent reactions of the isomeric imine. It was found that the isomerization reactions occur over virtually all of the hydrogenation catalysts studied, while their respective activities for the imine isomerization decreases in the order Ni = Co > Ru > Pt = Rh > Pd.

Isomerization and Deuterium Scrambling Evidence for a Change in the Rate-Limiting Step during Imine Hydrogenation by Shvo's Hydroxycyclopentadienyl Ruthenium Hydride

Hydroxycyclopentadienyl ruthenium hydride 5 efficiently reduces imines below room temperature. Better donor substituents on nitrogen give rise to faster rates and a shift of the rate-determining step from hydrogen transfer to amine coordination. Reduction of electron-deficient N-benzilidenepentafluoroaniline (8) at 11 degrees C resulted in free amine and kinetic isotope effects of k(OH)/k(OD) = 1.61 +/- 0.08, k(RuH)/k(RuD) = 2.05 +/- 0.08, and k(RuHOH)/k(RuDOD) = 3.32 +/- 0.14, indicative of rate-limiting concerted hydrogen transfer, a mechanism analogous to that proposed for aldehyde and ketone reduction. Reduction of electron-rich N-alkyl-substituted imine, N-isopropyl-(4-methyl)benzilidene amine (9), was accompanied by facile imine isomerization and scrambling of deuterium labels from reduction with 5-RuDOH into the N-alkyl substituent of both the amine complex and into the recovered imine. Inverse equilibrium isotope effects were observed in the reduction of N-benzilidene-tert-butylamine (11) at -48 degrees C (k(OH)/k(OD) = 0.89 +/- 0.06, k(RuH)/k(RuD) = 0.64 +/- 0.05, and k(RuHOH)/k(RuDOD) = 0.56 +/- 0.05). These results are consistent with a mechanism involving reversible hydrogen transfer followed by rate-limiting amine coordination.

Mechanisms of acid-catalyzed Z/E isomerization of imines.

The kinetics and mechanism of acid-catalyzed Z/E isomerization of O-methylbenzohydroximoyl chloride (1Za and 1Ea), methyl O-methylbenzohydroximate (1Zb and 1Eb), ethyl O-methylbenzohydroximate (1Zc and 1Ec and five para and meta substituted derivatives), O-methylcinnamohydroximoyl chloride (2Za and 2Ea), and methyl O-methylcinnamohydroximate (2Zb and 2Zb) have been investigated. The kinetics of Z/E isomerization of these imines have been studied in glacial acetic acid (1Ea and 1Zc) and in dioxane solutions containing HCl, trifluoromethanesulfonic acid, or tetrafluoroboric acid (1Ea, 1Zb, 2Ea, and 2Zb). The isomerization takes place by either (a) rotation about the carbon-nitrogen double bond of the protonated imine (iminium ion rotation) or (b) nucleophilic attack on the protonated imine to form a tetrahedral intermediate that undergoes stereomutation and loss of the nucleophile (nucleophilic catalysis). The hydroximoyl chlorides 1Eaand 2Ea only isomerize by the nucleophilic catalysis mechanism. The hydroximate 1Zb appears to be capable of isomerizing by either mechanism. The hydroximate 2Zb may be isomerizing only by iminium ion rotation. Theoretical calculations support the notion that increased conjugation in the protonated imine increases the rate of iminium ion rotation.

ChemInform Abstract: Isomerization of Imines Catalyzed by Ruthenium‐Hydride Complexes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Isomerization of Imines Catalyzed by Ruthenium-Hydride Complexes

Abstract Imine isomerization via [1,3]-hydrogen shift catalyzed by dihydrido(dinitrogen)tris(triphenylphosphine)ruthenium(II) or dihydridotetrakis(triphenylphosphine)ruthenium(II) complexes is described. In toluene under hydrogen atmosphere, ruthenium-dihydride complexes could cause the isomerization of ketimines to aldimines effectively.

ChemInform Abstract: Efficient Transamination under Mild Conditions: Preparation of Primary Amine Derivatives from Carbonyl Compounds via Imine Isomerization with Catalytic Amounts of Potassium tert‐Butoxide.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Efficient Transamination under Mild Conditions: Preparation of Primary Amine Derivatives from Carbonyl Compounds via Imine Isomerization with Catalytic Amounts of Potassium tert-Butoxide

1,3-Prototropic rearrangement of N-diphenylmethanimines was successfully performed with a catalytic amount of potassium tert-butoxide. This procedure can also be used with aliphatic and aromatic aldimines and was extended to the isomerization of (1R)-camphorquinone monoimine and N-(4-methoxyphenyl)-4-phenyl-3-iminoazetidin-2-one. The isomerized imines were easily hydrolyzed and isolated as Cbz derivatives.

Intramolecular 1,3-dipolar cycloaddition at the periphery of heterocyclic systems. Part 3. A facile hydrazone-azomethine imine isomerization at the periphery of pyridine and pyrido[1,2- a]pyrimidine systems

The phenylhydrazones of 2-(alk-2-enylamino)-4-oxo-4 H-pyrido[1,2- a]pyrimidine-3-carbaldehydes and 4-(alk-2-enylamino)-1,6-dimethyl-2-oxo-1,2-dihydropyridine-3-carbaldehydes underwent the thermally induced 1,3-dipolar cycloaddition leading to a mixture of the fused pyrazolidine and pyrazoline derivatives under extremely mild conditions. For the observed facile hydrazone-azomethine imine isomerization, we proposed an intramolecularlly assisted process similar to that for the facile oxime-nitrone isomerization in these systems; the intramolecular proton transfer from the the protonated alkenylamino and/or carbonyl moieties to the imine nitrogen facilitated the generation of the azomethine imine intermediates.

ChemInform Abstract: Asymmetric Imine Isomerization in the Enantioselective Synthesis of Chiral Amines from Prochiral Ketones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Computational studies on isomerization of imine from penicillin and electron transfer by carboxyiminium derived from β-lactams

Fused-ring β-lactams readily form imine carboxylic acids upon binding to cell-wall enzymes. It has been proposed that part of the antibiotic action of β-lactams may involve electron transfer by the corresponding iminium form of these derivatives. In the case of penicillin, ring opening leads to a compound which might be expected to isomerize to two stable conjugated species. One conversion yields a conjugated carboxyimine, while the other results in loss of the imine functionality. Semiempirical calculations were carried out to determine which isomerization is favored. The heats of formation for the initial compound, the final isomers, their protonated forms, as well as the intermediates involved were calculated using MNDO. Whereas one conjugated isomer (the imine) is thermodynamically more stable, the other (an enamine) is favored kinetically. Molecular orbital energies (LUMO's) for these structures show that the thermodynamically favored isomer has greater potential to participate in electron transfer than the kinetically favored product. In addition, calculations on simple molecules bearing structural similarity to the thermodynamically preferred isomer reveal that electron transfer is facilitated if the acid portion of the carboxyiminium remains protonated and is enhanced by the presence of sulfur in the structure.

A comparative study of neighbouring group effects on the isomerization of imines in platinum-imine complexes by 1H, 13C, 31P and 195Pt NMR spectroscopy

195Pt-, 31P-, 13C- and 1H-chemical shifts are reported for the first time for complexes of the type trans-[PtCl 2 (η 2-C 2H 4) (imine)], I, trans-[PtCl 2 (η 2-C 2H 4) (amine)] II, and trans-[PtCl 2(PR′ 3) (imine)] III (the imine ligand being derived from cyclopropyl-2-thienylketone and primary amines; PR′ 3 = PBu n 3 and PPh 3; amine; the amine ligand obtained by the reduction of the appropriate imine). The use of multinuclear spectroscopy provides strong evidence for E-Z isomerization of imine ligands coordinated to platinum (II) of the type trans-[PtCl 2 (η 2-C 2H 4)(imine)]. Tertiary phosphine ligands trans to imine ligand ( III) are not strongly labilizing groups, in contrast to η 2-C 2H 4, which shows a strong labilizing effect. The effect of neighbouring groups on E-Z isomerization indicates that increase of the bulky substituents close to the imino group tends to increase the rate of isomerization, and increasing the degree of substitution on the imine carbon atoms slows the rate of isomerization. Furthermore, addition of a trace of amine will catalyze the E-Z isomerization. Also, isomerization takes place in the liquid state to give one isomer during the coordination with platinum.

Isomerization of imines in platinum-imine complexes

Multinuclear 1H, 13C and 195Pt spectroscopy provides strong evidence for E-Z isomerization of imine ligands coordinated to platinum(II) of the type trans [PtCl 2(η 2-C 2H 4)(imine)].

ChemInform Abstract: Dynamic Stereochemistry of Imines and Derivatives. Part 19. Mutarotation and E‐Z Isomerization of Chiral Imines in [2H4]Methanol Solution.

ChemInform Abstract: Dynamic Stereochemistry of Imines and Derivatives. Part 19. Mutarotation and E‐Z Isomerization of Chiral Imines in [2H4]Methanol Solution.

Dynamic stereochemistry of imines and derivatives. 19. Mutarotation and E-Z isomerization of chiral imines in [2H4]methanol solution

La mutarotation des phenyl-1' ethylimine d'acetophenone et d'acetonaphtone-1 dans CD 3 OD est une isomerisation cis-trans et non pas une tautomerie en enamine