Intramolecular Transformation Research Articles

Reactivity and Selectivity of Ortho-Metalated Rhodium(II) Complexes in C−H Insertion Reactions of α-Diazo Compounds

Regioselective intramolecular C−H insertion reactions of α-diazo β-keto esters and α-diazo ketones are mediated by Rh2[OOCR]4-x[PC]x (x = 1, 2; PC = ortho-metalated phosphine; R = CH3, C3F7). In particular, the intramolecular transformation of 1-diazo-5-methyl-3-propyl-2-hexanone catalyzed by Rh2[OOCCH3]2[PC]2 (PC = (C6H4)P(C6H5)2, head-to-tail (H−T) configuration) afforded only the tertiary C−H insertion product. By comparison, no C−H insertion reaction was promoted by doubly metalated complexes with a head-to-head (H−H) configuration. Rh2[OOCR]3[PC] compounds were found to be less suited for these type of reactions.

High pressure-controlled intramolecular-twist of flexible molecules in solid polymers

We report the effect of pressure on fluorescence of two flexible dye molecules of a series of para-substituted benzylidenemalononitriles dissolved in solid poly(methyl methacrylate). Under pressure these molecules exhibit a remarkable increase of intensity and slowing of excited state decay. We show that these changes can be well explained by a kinetic model in which the pressure is assumed to control the barrier for the intramolecular transformation of the flexible molecules in their excited state.

Mechanisms of synthesis of maleic and succinic anhydrides by carbonylation of acetylene in solutions of palladium complexes

The mechanism of synthesis of maleic and succinic anhydrides from acetylene and CO in the PdBr2−LiBr-organic solvent catalytic system was studied using the procedure of advancement and discrimination of hypotheses. The hypotheses were obtained using the data bank on elementary steps and the Combl combinatorial program. The discrimination of the hypotheses was based on the data of NMR and IR spectroscopy, studies of isotope exchange, the role of potential organic intermediates, the kinetic isotope effect, and one-factor kinetic experiments. The most probable mechanism of synthesis of maleic anhydride includes insertion of acetylene and CO into the Pd−Pd bond of the PdI complex, which is formed from PdII at the initial step of the process. Succinic anhydride results from the intramolecular transformation of the hydride complex of palladium and maleic anhydride. The palladium hydride complexes detected in the contact solution apparently play the crucial role in the conjugation of oxidation, reduction, and addition type reactions.

Intramolecular electron transfer between tryptophan radical and tyrosine in oligoproline-bridged model peptides and hen egg-white lysozyme.

Long range electron transfer (LRET) across protein matrix underlies all one-electron cellular redox reactions. Elucidation of molecular electron transfer pathways and parametrization of their relative efficiency is one of the most challenging problems in the studies on LRET in proteins. In this paper results of pulse radiolysis investigations on kinetics of LRET accompanying intramolecular radical transformation Trp. --> TyrO. in model peptides built of tryptophan and tyrosine bridged by an oligoproline fragment are reviewed, along with an interpretation of the observed distance dependence of the rate of LRET in terms of conformational properties of the peptides, and partitioning of LRET between electron transfer pathways through space and through peptide backbone. This review on model peptide systems is supplemented with recapitulation of similar studies on the same intramolecular transformation in hen egg-white lysozyme, which allowed to identify Trp./Tyr redox pairs and associated electron transfer pathways involved in LRET in this protein.

Dependence of the fluorescence parameters and the intersystem crossing rate constant on the orbital nature of the s 1 state of catacondensed aromatics

Fluorescence properties of nine specially chosen aromatic compounds are studied experimentally at room temperature (293 K). The compounds, which are from the catacondensed class are arranged in such a way that odd numbered compounds reveal the 1 L b→ 1 A fluorescence, while even numbered compounds show the 1 L a→ 1 A fluorescence. All compounds are family related in π-structure and are of the same degree of planarity and rigidity. The quantum yield of fluorescence γ, and the decay times τ f, of nondeaerated and deaerated cyclohexane solutions are measured. The oscillator strength f e, the fluorescence rate constant K f, natural lifetimes τ 0 T and intersystem crossing rate constant K ST, are calculated. The lowest 1 L b and 1 L a singlet and 3 L a triplet (77 K) levels are determined. Investigations showed that transition from a catacondensed molecular which shows the 1 L a→ 1 A fluorescence to a family related in π-structure molecular which reveals the 1 L b→ 1 A fluorescence is accompanied by certain changes of all fluorescence parameters: γ is usually decreasing, τ f is increasing, K f is decreasing, FWRE of the fluorescence spectrum is decreasing and, moreover, K ST is also decreasing, sometimes very significantly. For example, K ST of phenanthrene is 28.5 times smaller than K ST of anthracene through S α-T 1 interval of phenanthrene is less than S p-T 1 interval of anthracene (7100 and 11660 cm −1 respectively). The systems of singlet and triplet levels of the compounds studied are simulated (PPP-CI) and triplet levels which mix with S 1 state are determined. The low K ST value of perylene is discussed and explained. To explain the observed phenomenon of decreasing values of K ST, the assumption is made that the matrix elements of the spin-orbit coupling between S α and T i state are much smaller than those between S p and T i states. The results obtained are important for further understanding of the influence of the orbital nature of S 1 state on the intramolecular transformation of light energy absorbed by a molecule.

Dreikomponentenreaktionen unter photochemischen bedingungen—der Transformationsweg des P 4-phosphors in der koordinationssphäre von Co-komplexen

The photolysis of [Cp x Co(CO) 2] (Cp x = Cp, Cp′ Cp″ Cp′″ Cp 5; Cp = η 5-C 5H 5, Cp′ = η 5-C 5H 4 tBu, Cp″ = η 5-C 5H 3 1Bu 2, Cp′″ = η 5-C 5H 2 1Bu 3, Cp 5 = η 5-C 5Ph 5) with P 4 phosphorus in the presence of [Cr(CO) 5(THF)] at ambient temperature yields the bicyclote-traphosphine complexes [Cp x Co(CO)( η 1:1-P 4)(Cr(CO) 5) 4] ( 1: Cp x = Cp, 2: Cp x = Cp′ 3; Cp x = Cp″), and as the main products, the cyclo-P 4 compounds [Cp x Co( η 4-P 4){Cr(CO) 5} 4] ( 4: Cp x = Cp, 5: Cp x = Cp′) and [Cp x Co( η 4-P 4){Cr(CO) 5} 3] ( 6: Cp x = Cp″ 7: Cp x = Cp′″, 8: Cp x = Cp 5), respectively. Studies of the reaction pathway show, that the bicyclotetraphosphines 1–3 are formed first followed by their intramolecular transformation in the cyclo-P 4 complexes 4–8. The coordination behavior of the cyclo-P 4 ligand as well as the relative nonparallel arrangement of the P 4 and the Cp x rings depend on the nature of the organic substituents of the Cp x ligands. The angle between the P 4 and the Cp x planes increases from 4 to 9° in the series Cp x = Cp″ < Cp′″ < Cp 5. Variable temperature 31P-NMR investigations reveal different rotation barriers due to the corresponding Cp x ligand ( 6: Δ G Tc ≠ = 39.1 kJ mol −1). 7 and 8 have a high tendency to lose [Cr(CO) 5]-groups in solution resulting in complexes with only one or two bound [Cr(CO)5]-fragments.

Significance of the intramolecular transformation of glutathione thiyl radicals to α-aminoalkyl radicals. Thermochemical and biological implications

R. Zhao, J. Lind, G. Merényi and T. E. Eriksen, J. Chem. Soc., Perkin Trans. 2, 1997, 569 DOI: 10.1039/A605727F

Dendrimers with 1,3,4‐oxadiazole units, 1. Synthesis and characterization

AbstractThe synthesis and characterization of two unsymmetrically substituted star‐shaped oxadiazoles and of a dendrimer of the first generation are described. The key step in the synthesis is the intramolecular ring transformation of aromatic tetrazoles. The well‐defined compounds form stable amorphous glasses with high glass transition temperatures up to 222°C. They are promising candidates for organic light emitting diodes.

Oxidation of methionine peptides by Fenton systems: the importance of peptide sequence, neighbouring groups and EDTA

We investigated the anaerobic oxidation of several Thr- and Met-containing di- and tri-peptides by Fenton systems, (NH4)2Fe(SO4)2/H2O2 and [FeII(EDTA)]2–/H2O2, respectively, and compared the respective product patterns with those obtained after oxidation with free radiation chemically generated hydroxyl radicals. The products obtained by the (NH4)2Fe(SO4)2/H2O2 system did not show any significant resemblance to product patterns characteristic for free hydroxyl radicals. In contrast, the [FeII(EDTA)]2–/H2O2 system generated a material balance which showed some similarity to the free hydroxyl radical-generated pattern. From a comparison of the relative reactivities of the various functional groups of the peptides with the quantities of products obtained, we conclude that for Thr Met, in particular at pH 6.3, a direct attack of a fraction of reactive oxygen species at the Met sulfur caused the formation of a sulfuranyl radical intermediate. This then underwent intramolecular coupled proton/electron-transfer with the protonated N-terminus to yield nitrogen-centered radical cations. The latter subsequently suffered heterolytic fragmentation of the Cα–Cβ bond of Thr to yield acetaldehyde. Such a pathway had previously been characterized for the oxidation of Thr-Met by free HO˙. The occurrence of such intramolecular radical transformation is taken as evidence that neighbouring group effects can operate during metal-catalysed peptide (and possibly protein) oxidation.

Binary and ternary complexes of nickel(II) with 2-aminomethylbenzimidazole and salicylaldehyde: kinetic and equilibrium studies

The complexation of NiII with 2-aminomethylbenzimidazole (L) has been investigated at 20–40 °C, I= 0.30 mol dm–3. Both monoprotonated and unprotonated ligands bind the metal ion to form [NiL]2+. and the rate and activation parameters for the formation and acid-catalysed dissociation of this chelate are calculated. In the presence of Salicylaldehyde (Hsal), a mixed-ligand complex. [NiL(sal)]+, is also formed as an intermediate which further condenses to the Schiff-base complex, [NiL′]+[HL′=N-(benzimidazol-2-ylmethyl)salicylideneimine]. The kinetics of the fast ternary complex formation and its slow intramolecular transformation to the Schifi base complex have been investigated at 25 °C. The presence of L in the co-ordination sphere of Ni2+ enhances the dissociation of [NiL(sal)]+ to [NiL]2+ and sal– with respect to [Ni(Sal)]+, as evidenced by the stability constants of [NiL(sal)]+ and [Ni(sal)]+. Calculations based on the values of ΔS° for the ionisation of H2L2+ and the formation of [NiL]2+combined with Saq°(H+) and Saq°(Ni2+) data yielded the values Saq°(H2L2+)–Saq°(L)= 110, Saq°(L)–Saq°(HL+)=–116 and Saq°([NiL]2+)–Saq°(L)=–294 J K–1 mol–1, which presumably reflect the varying solvent-ordering effects of L, HL+, H2L2+ and [NiL]2+.

The unusual Stevens type rearrangements of some dialkyl sulfides on a Rh–Rh bond

The coordinative addition of dimethyl sulfide to (C5H5)2Rh2(µ-CO)(µ-CF3C2CF3) is followed by an intramolecular transformation to give (C5H5)2Rh2(µ-SCH2Me){µ-C(CF3)CH(CF3)}, and the corresponding reaction with Et2S gives a related complex with a chiral bridging sulfido group SCHMeEt.

Leaving group based intramolecular glycoside bond formation

Sterically crowded β-hydroxy-substituted glucosyl carboxylates 4α,β furnish with strong alkylating agents 5a-c in the presence of base diastereoselectively α- or β-glucosides 6a-c, respectively; in addition, β-lactone 7 is formed. The reaction is discussed in terms of an intramolecular ortho-ester transformation.

Pulse radiolysis studies of intramolecular electron transfer in model peptides and proteins. IV. Met/S:.Br-->Tyr/O. radical transformation in aqueous solution of H-Tyr-(Pro)n-Met-OH peptides.

The intramolecular radical transformation Met/S:.Br-->Tyr/O. in aqueous peptides H-Tyr-(Pro)n-Met-OH, n = 0-3, was investigated in the temperature range of 283-328 K by pulse radiolysis. Corresponding first-order rate constants and thermodynamic parameters of activation of electron transfer, Ea and delta S++, were determined from kinetic data. The rate constants of the reaction were found to decrease exponentially with the number of Pro units and the distance between CR atoms of the terminal amino acids, with a correlation coefficient alpha = 3.2 +/- 0.5 nm-1 at 298 K. Its value appeared to be temperature dependent suggesting the occurrence of thermally induced conformational changes in the peptides. Analysis of experimental data in terms of known conformational properties of the peptides indicates that apparent values of alpha, Ea and delta S++ are probably complicated functions of conformation and thermodynamic stability of the oligoproline bridge, varying with the number of Pro residues, and of intramolecular hydrophobic interactions between side chains of tyrosine and methionine. Estimation of the relative efficiency of electron transfer pathways through the peptide backbone and through direct and/or water mediated contact between groups bearing radical sites led to the conclusion that partitioning of electron transfer along these pathways is likely to occur.

Intramolecular transformation reaction of the glutathione thiyl radical into a non-sulphur-centred radical: a pulse-radiolysis and EPR study.

The thiyl radical derived from glutathione (GSH) is shown to decay rapidly in aqueous solution by intramolecular rearrangement reactions into the non-sulphur-centred radical 1. The reaction is induced by OH- with a rate constant of 5 x 10(9) dm3 mol-1 and is also observable at near-neutral conditions (at physiological pH values around 7.5 the rate of formation of 1 amounts to approximately 1 x 10(3) s-1). The activation enthalpy and entropy at pH 8.4 and 20 degrees C were found to be 26.7 kJ mol-1 and -77 J mol-1 K-1, respectively. Radical 1 was unequivocally identified by EPR as the alpha-amino radical at the glutamyl residue of GSH. It is relatively long-lived with typical bimolecular decay rate constants of the order of (2-20) x 10(6) dm3 mol-1 s-1. At higher GSH concentrations the formation of 1 is retarded but not inhibited. All radicals, sulphur- as well as non-sulphur-centred ones are connected via equilibria, partly under the action of 'repair' processes of GSH. These repair processes, however, are slow (k much less than 1.4 x 10(5) dm3 mol-1 s-1). The equilibria are established quite rapidly and were found to be far on the side of the non-sulphur-centred radical under all conditions employed. Radical 1 possesses reducing properties as evidenced by its fast reaction with 4-nitro-acetophenone (PNAP) to yield PNAP.- (k = 7 x 10(8) dm3 mol-1 s-1).

Reactions of [Cp*RuOMe]2. 7. Intramolecular transformation of a RuOCH3 unit into a Ru(CO)H unit: crystal and molecular structure of Cp*Ru(.mu.-H)2(.mu.-CO)RuCp*

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTReactions of [Cp*RuOMe]2. 7. Intramolecular transformation of a RuOCH3 unit into a Ru(CO)H unit: crystal and molecular structure of Cp*Ru(.mu.-H)2(.mu.-CO)RuCp*Byung Sun Kang, Ulrich Koelle, and Ulf ThewaltCite this: Organometallics 1991, 10, 8, 2569–2573Publication Date (Print):August 1, 1991Publication History Published online1 May 2002Published inissue 1 August 1991https://doi.org/10.1021/om00054a014RIGHTS & PERMISSIONSArticle Views191Altmetric-Citations21LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (590 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Intramolecular acetalization of 5-hydroxy ketones and enones. A novel transformation of important prostaglandin intermediates under acidic conditions

Intermediates in the synthesis of ω-tetranor 16-aryloxy prostaglandins, which are 5-hydroxy enones, undergo quantitative intramolecular transformation into cyclic methyl acetals in acidic methanolic solution. The reaction proceeds via the corresponding 5-hydroxy-3-methoxy ketones, which partly exist as hemiacetals. The structure of the compounds investigated was elucidated by 1H NMR spectroscopy and by X-ray analysis of the acetal (11).

A TWO-STEP MECHANISM FOR THE INCLUSION REACTIONS OF α-CYCLODEXTRIN WITH MONO ALKYL-SUBSTITUTED HYDROXYPHENYLAZO DERIVATIVES OF SULFANILIC ACID

Abstract Kinetic studies on the inclusion reactions of the title azo compounds with α-cyclodextrin (α-CDx) in aqueous solution by means of the stopped-flow method reveal a two-step inclusion mechanism involving a fast binding process of the guest compounds to α-CDx followed by the slow intramolecular transformation of the intermediate inclusion complex. Activation parameters for each step were determined.

Matrix isolation of free radicals from carbohydrates. II. Reactions of H. with glucose and derivatives in acidic glasses.

Photolytically produced H.-atoms in 6 mol dm-3 H2SO4/H2O glasses trapped at 77 K react upon annealing to 130 K with dissolved carbohydrates to form carbon-located free radicals by abstraction of carbon-bound protons. Analysis of electron spin resonance (e.s.r.) spectra at various annealing stages from alpha- and beta-D-glucose together with 6,6-d2-D-glucose, 6-deoxy-D-glucose, 2-deoxy-D-glucose, glucose-1-phosphate, D-xylose, D-allose and D-mannose indicates radical formation at all possible carbon sites with a strong preference for C1 and a somewhat enhanced contribution of C4 over the statistical expectation. The corresponding component spectra are analysed either by spectra isolation or simulation and their parameters are given. Intramolecular radical transformation at temperatures of 140-160 K is explained by acid-catalysed H2O-elimination. The findings are discussed in relation to the radiation-chemistry of aqueous glucose solutions. We thus show that the system of photolyzed Fe2+ in acidic glasses at low temperatures containing 10 mmol dm-3 carbohydrate is suitable for studying H(D.)-reactions by means of e.s.r. spectroscopy. Unlike previously used glasses containing carbohydrates, contributions of oxidation and reduction by direct effects or mixtures of direct and indirect effects and phase-effects due to incomplete glass formation are avoided.

Synthesis of cyclopentano[c]-s -triazoles by the intramolecular ring transformation of 1,3,4-oxadiazoles

Cyclopentano[c]-s-triazoles were synthesized by intramolecular ring transformation starting from y-keto-l,3,4-oxadiazoles 5 and 9. The required functionality for this intramolecular reaction was established by (i) the reaction of lithiated 2-methyl-l,3,4-oxadiazole 4 with the methyl enol ether of α-bromo ketones followed by hydrolysis; (ii) reductive amination of γ-ketones 5 and 9 to further reorganized hydrazide 7 and y-amino-l,3,4-oxadiazole 9 with NaBH 3CN; and (iii) pyrolysis of 7 and γ at 280° (5 mmHg) to the cyclopentano[ c]- s-triazoles 8 and 11. By the same treatment, the S-connected analogue 2 afforded the desired fused s-triazole 17.

Synthesis of fused s-triazoles from 2-methanesulfonyl-5-phenyl-1,3,4-oxadiazole and binucleophilic reagents by means of intramolecular ring transformation.

2-Methanesulfonyl-5-phenyl-1, 3, 4-oxadiazole (4) reacted with 3-aminopropanol and 2-aminoethanethiol in the presence of triethylamine to give displaced and rearranged products 2-(5, 6-dihydro-4H-1, 3-oxazin-2-yl)-(6b) and 2-(2-thiazolin-2-yl) benzhydrazide (9), which were further cyclodehydrated by heating to give the corresponding fused s-triazoles (7) and (10), respectively. In the case of the reaction with a diaminoalkane only the 1 : 2 adduct (8) was obtained.