bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cope Rearrangements versus Retro Diels‐Alder Reactions
Authors: Beck Karin , Hoffman Petra , Hünig Siegfried 
Published: July 2007

AbstractThe two isomeric [4+2] cyclo‐adducts from two different 1,3‐dienes may result from direct cycloadditions as well as from Cope rearrangements (Scheme 1). This general question is tackled by employing two energetically different types of dienes, protonated pyrazolines (1H+, 2H+) or dihydropyridazines (3H+), prepared in situ from their trimers and alicyclic (4–6) or aliphatic (7–9) 1,3‐dienes. Depending on structural features and conditions (amount of acid, reaction time), various ratios of the two isomeric [4+2] cycloadducts A and B are obtained; A and B are azo compounds 10, 14, 16, 20, 22, 24, 27, 32, 34, 36–39, 41, 42, pyrazolines endo‐11, endo‐13, endo‐15, endo‐endo‐17, endo‐18, endo‐19, 21, 23, 25, 26, 28, and hydropyridazines 31, endo‐33, endo‐35, 40 and 43 (Schemes 3, 4). These results were backed by others from acid‐catalyzed isomerizations, trapping experiments, and calculations of the equilibria (ΔΔH) between the isomers (by analogy with the corresponding olefins). A critical discussion reveals: a) Azo compounds 20, 22, 24, 27, 34, 38, and 42 must result from a [4++2] cycloaddition with inverse electron demand, whereas hydropyridazines endo‐33, endo‐35, 40, and 43 originate from a [4+2+] cycloaddition with normal electron demand. b) All isomerizations occur by a [3,3] sigmatropic rearrangement; [4+2] cycloreversion is energetically disfavored. c) A clear‐cut distinction between the [4++2] or [4+2+] cycloaddition reaction routes to the energetically well‐balanced systems 10→endo‐11 and 12→endo‐13 is not possible. d) The two cycloadditions may well favor a nonconcerted reaction through an allylic cationic intermediate which also governs the [3,3] rearrangements (Scheme 8).
Type B Semiconductor Photocatalysis: The Synthesis of Homoallyl Amines by Cadmium Sulfide‐Catalyzed Linear Photoaddition of Olefins and Enol/allyl Ethers to N‐Phenylbenzophenone Imine
Authors: Keck Helmut , Schindler Wolfram , Knoch Falk , Kisch Horst 
Published: July 2007

AbstractHomoallyl amines were synthesized by visible‐light irradiation of CdS powder in the presence of N‐phenylbenzophenone imine and cyclohexene, 2,3‐dihydrofuran, 2,5‐dihydrofuran, 3,4‐dihydropyran, 2‐pentene, cyclopentene, 1‐methylcyclohexene, or α‐pinene. The structures of the products from the last three olefins were determined by single‐crystal X‐ray analysis to prove that C‐alkylation of the imine had occurred. Thus, the reaction is formally an insertion of the imine into an allylic C‐H bond of the olefin. It is proposed that a photogenerated electron–hole pair reduces the imine to an α‐aminodiphenylmethyl radical and oxidizes the olefin with concomitant deprotonation to the corresponding allyl radical. Heterocoupling of these intermediates affords the final addition product. The overall reaction is therefore classified as type B semiconductor photocatalysis. The presence of acetic acid accelerates the reaction by rendering the reduction potential of the imine more positive. In the series 2,5‐dihydrofuran/cyclopentene/3,4‐dihydropyran, the decrease in apparent quantum yield with increasing driving force of olefin oxidation points to a significant contribution of secondary back electron transfer.
In Search for Mononuclear Helical Lanthanide Building Blocks with Predetermined Properties: Lanthanide Complexes with Diethyl Pyridine‐2, 6‐Dicarboxylate
Authors: Renaud Fabien , Piguet Claude , Bernardinelli Gérald , Bünzli Jean‐Claude G. , Hopfgartner Gérard 
Published: July 2007

AbstractThe ligand diethyl pyridine‐2, 6‐dicarboxylate (L5) reacts with LnIII in acetonitrile to successively give the complexes [Ln(L5)i]3+ (Ln = La to Lu, i = 1‐3). Spectroscopic investigations (ES‐MS, UV/Vis, NMR) show that the 1:3 complexes [Ln(L5)3]3+ have poor stability in solution and exist as a mixture of rapidly interconverting conformers. Variable‐temperature NMR data show that the helical P→M interconversion and dynamic on‐off equilibria of the ester side arms both control the observed average structure in solution. Contrary to similar lanthanide building blocks possessing benzimidazole or carboxamide side arms, [Eu(L5)3]3+ has a sizable quantum yield in anhydrous acetonitrile; this has been attributed to an improved ligand → EuIII energy transfer resulting from a good energetic match between the ligand‐ and metal‐centered excited states. Pure 1:3 complexes cannot be isolated in the solid state, but crystalline 1:2 complexes [Ln(L5)2](TfO)3.nH2O have been prepared. The X‐ray crystal structure of [Eu(L5)2(TfO)2(OH2)]TfO (1) reveals two meridionally tricoordinated ligands L5, but the long Eu‐O(ester) bonds imply only weak interactions between the carbonyl groups of the ester side arms and EuIII, providing a limited protection of the metallic site. The photophysical studies show that nonacoordinate EuIII in 1 binds an additional water molecule to give a decacoordinate complex in the solid state, thus confirming the accessibility of the metallic site for further complexation.
Synthesis of Pyrazinoporphyrazine Derivatives Functionalised with Tetrathiafulvalene (TTF) Units: X‐Ray Crystal Structures of Two Related ttf Cyclophanes and Two Bis(1,3‐Dithiole‐2‐Thione) Intermediates
Authors: Wang C. S. , Bryce M. R. , Batsanov A. S. , Howard J. A. K. 
Published: July 2007

AbstractThe pyrazinoporphyrazine system 13 (metal‐free, zinc and copper derivatives) has been synthesised by tetramerisation of 2,3‐dicyanopyrazine monomer unit 10. The structure of 13a‐c has been established by 1H NMR spectroscopy, UV/Vis spectrophotometry, MALDI‐TOF mass spectrometry, cyclic voltammetry and differential pulse voltammetry. The electrochemical redox behaviour of 13a‐c is strongly solvent dependent. The expected two‐stage oxidation of the tetrathiafulvalene (TTF) units of 13a‐c was observed in a range of solvents; in addition, oxidation and reduction of the pyrazinoporphyrazine core of the metal‐free derivative 13a was detected in benzonitrile. On excitation of 13 in the Q‐band region no fluorescence was observed, which is presumably the consequence of intramolecular charge transfer between the TTF moieties and the excited state of the central porphyrazine. Molecular modelling studies on 13a and 13c are reported. During the course of this work, the novel TTF macrocycles 11 and 20 were synthesised; their X‐ray crystal structures reveal severely bent TTF units, the conformations of which are discussed in detail. The X‐ray crystal structures of the bis(1,3‐dithiole) systems 15 and 18 have also been determined.
N‐Alkyloxycarbonyl‐3‐aryloxaziridines: Their Preparation, Structure, and Utilization As Electrophilic Amination Reagents
Authors: Vidal Joëlle , Damestoy Stéphanie , Guy Laure , Hannachi Jean‐Christophe , Aubry André , Collet Andreé , Aubry André 
Published: July 2007

AbstractThis paper reports the synthesis of a series of N‐protected oxaziridines (N‐Moc, Boc, Z or Fmoc) and discusses their ability to deliver their N‐alkoxycar‐bonyl fragment to amines, enolates, sulfur, and phosphorus nucleophiles (electrophilic amination). These oxaziridines are prepared by oxidation of the corresponding imines with oxone or anhydrous MCPBA lithium salt as the source of oxygen. They transfer their N‐protected fragment to primary and secondary amines to give protected hydrazines in fair to excellent yield. The nitrogen transfer to free amino acids (in form of their R4N+ salts) is particularly fast, even at low temperature, providing L (or D) N‐protected α‐hydrazino acids. Enolates are C‐aminated to give N‐protected α‐amino ketones, esters, or amides in modest yield, due to a side aldol reaction of the unreacted enolate with the released benzaldehyde. With tertiary amines (Et3N), sulfides (PhSMe), and phosphines (Ph3P), amination and oxidation proceed in a parallel way; the amount of amination product increases when the temperature is lowered (kinetic control). Some of the factors that can orient the oxaziridine reactivity towards amination or oxidation of nucleophiles are considered.
Synthesis and Properties ofO‐Glycosyl Calix[4]Arenes (Calixsugars)
Authors: Dondoni Alessandro , Marra Alberto , Scherrmann Marie‐Christine , Casnati Alessandro , Sansone Francesco , Ungaro Rocco 
Published: July 2007

AbstractModelO‐glycosylation reactions at either rim of calix[4]arenes are described with the aim of providing access to a new family of carbohydrate‐containing calixarene derivatives named calixsugars. One or two sugar moieties (D‐mannofuranose and D‐glucopyranose) were introduced at the lower rim of the parent calix[4]arene by glycosylation of the phenolic hydroxyl groups by means of a Mitsunobu reaction. Tetrapropoxy calix[4]arenes bearing two or four hydroxymethyl groups at the upper rim were coupled with perbenzoylated thioethyl D‐galactoside and D‐lactoside in the presence of the thiophilic promoter copper(III) triflate. In this way β‐linked bis‐ and tetrakis‐O‐galactosyl calix[4]arenes were obtained in good yield, the latter showing some solubility in water. For theO‐lactosyl derivatives only the bis‐substituted compound could be obtained because of the competing formation of an intramolecular ether linkage between 1,3‐hydroxymethyl groups. Preliminary binding studies showed some affinity of the galactose‐containing calixsugars toward charged carbohydrates and dihydrogen phosphate anion.
Gas‐Phase Reactions at Low Temperatures: Towards Absolute Zero
Authors: Smith Ian W. M. , Sims Ian R. , Rowe Bertrand R. , Rowe B. R. 
Published: July 2007

AbstractVery recently, methods have been developed for studying the rates of chemical reactions between electrically neutral species in the gas phase at temperatures as low as 13 K. Here we review this exciting development in gasphase chemical kinetics. Emphasis is placed on the importance of the information which the experiments have provided, both from the viewpoint of posing new questions about the factors which control chemical reactivity and because of their relevance to the modelling of molecular synthesis in interstellar clouds.
Electrochemically Induced Molecular Motions in Pseudorotaxanes: A Case of Dual‐Mode (Oxidative and Reductive) Dethreading
Authors: Asakawa Masumi , Ashton Peter R. , Balzani Vincenzo , Credi Alberto , Mattersteig Gunter , Matthews Owen A. , Montalti Marco , Spencer Neil , Stoddart J. Fraser , Venturi Margherita 
Published: July 2007

AbstractThe electrochemical and spectroscopic properties of a pseudorotaxane formed in acetonitrile solution by self‐assembly of a wire‐type electron donor based on the tetrathiafulvalene unit and the cyclobis(paraquat‐p‐phenylene) tetracationic electron acceptor have been investigated. We show that a) reversible dethreading/rethreading cycles of the pseudorotaxane can be performed by either oxidation and successive reduction of the electron‐donor wire or reduction and successive oxidation of the electron‐accepting tetracationic cyclophane, and b) because of this special behavior, the input (electrochemical)/output (absorption spectrum) characteristics of this molecular‐level system correspond to those of an XNOR logic gate.
Oligonucleotide Analogues with 4‐Hydroxy‐N‐Acetylprolinol as Sugar Substitute
Authors: Ceulemans Griet , Van Aerschot Arthur , Wroblowski Berthold , Rozenski Jef , Hendrix Chris , Herdewijn Piet 
Published: July 2007

AbstractModified oligonucleotides incorporating trans‐4‐hydroxy‐N‐acetyl‐L‐prolinol (trans‐4‐HO‐L‐NAP) or its D‐analogue as sugar substitute were synthesised with adenine and thymine as nucleobases. All‐adenine oligonucleotides built from (2S,4S) or (2R,4R)‐cis‐4‐hydroxy‐N‐acetylprolinol were likewise prepared. Hybridisation studies revealed that heterocomplexes formed between polyU and homochiral trans‐4‐hydroxy‐N‐acetylprolinol‐based oligomers of the same as well as of opposite chirality (polyU/trans‐DA*13 and polyU/trans‐LA*13). The former, however, were triple‐stranded. Other complexes with ribonucleic acids were polyA/trans‐LT*13 and polyU/cis‐LA*13. Heteroduplexes with deoxynucleic acids were formed between trans‐LA*13 and oligothymidylate. Interaction was also observed for cis‐LA*13 and oligothymidylate, but not with the D‐hydroxyprolinol analogues. Microcalorimetry proved this interaction to be the formation of a triple‐stranded complex. Two heteroduplexes, trans‐LA*13/dT13 and trans‐LA*13/polyU, had similar or slightly increased stability when compared to the natural dA13/dT13 or dA13/polyU systems. Microcalorimetry clearly indicated the formation of a duplex, in contrast to interactions with N‐acetylprolinol oligonucleotides of different stereochemistry. Moreover, the enthalpy change was of the same magnitude but the association constant was slightly lower. Natural nucleic acids thus clearly prefer hybridisation with L‐hydroxyprolinol oligomers over D‐hydroxyprolinol oligomers. For the series investigated, the L‐trans oligomers (Figure 1) seem best to mimic natural oligonucleotides. These modified oligonucleotides formed homocomplexes if both strands were of the same chirality, that is, homocomplexes formed between trans‐LA* and trans‐LT* and between trans‐DA* and trans‐DT*, reflecting the isochiral pu‐py pairing found in natural nucleic acids. Once more, however, calorimetry proved these to be triplex interactions. Heterochiral pairing was not observed between modified oligonucleotides, but only between modified oligonucleotides and natural polyU. The thermal stabilities of these heterochiral complexes differed clearly.
Mechanisms and Stereochemistry of Acid‐Induced Ring Opening of Optically Active 1,2‐Propene Oxides in the Gas Phase
Authors: Troiani Anna , Filippi Antonello , Speranza Maurizio 
Published: July 2007

AbstractThe acid‐induced ring opening of (S)‐(—)‐1,2‐propene oxide (1S) and (R)‐(+)‐1,2‐propene oxide (1R) has been investigated in gaseous CH4 and CH3F at 720 torr and in the presence of a nucleophile, NuOH (Nu = H or CH3). The mechanism of the ring‐opening reaction has been assessed by modulating the composition of the gaseous mixture. Two reaction pathways are operative in the gas phase, both proceeding through complete inversion of configuration of the reaction center. A first process is detectable only in the CH3F/H2O systems and takes place within a persistent proton‐bound complex generated by interaction of the epoxide with the CH3OH+2 ion, formed by methylation of H2O with (CH3)2F+. Such an intracomplex ring‐opening pathway proceeds through proton transfer from the CH3OH+2 ion to the epoxide followed by motion of the neutral CH3OH moiety around the 1‐H‐oxonia‐2‐methyl‐cyclo‐propane structure (H‐1R or H‐1S) (k<108 s‐1) before attacking the ring carbons from the rear. In all the other systems with added CH3OH, this intracomplex pathway is preceded by a faster “extracomplex” pathway involving the attack of an external CH3OH molecule on the proton‐bound adduct. The regioselectivity of the intracomplex process is similar to that of the extracomplex pathway. Both are characterized by a slight preference for the Cβ center of H‐1 R (or H‐1S) (extra‐complex path regioselectivity: α/β = 0.72±0.05; intracomplex path regioselectivity: α/β = 0.71±0.05). The regioselectivity of H‐1 R (or H‐1S) is substantially different from that of the 1‐Me‐oxonia‐2‐methyl‐cyclopropanes (Me‐1 R or Me‐1 S) toward the same nucleophile NuOH (α/β = 4.1±0.35 (Nu = H); 2.28±0.16 (Nu = CH3)). This difference is attributed to a transition structure wherein the Cα–O bond rupture increases from H‐1 R (or H‐1 S) to Me‐1 R (or Me‐1 S) and in passing from CH3OH to H2O. The regioand stereoselectivity of the gas‐phase acid‐induced ring opening of 1 S and 1 R are compared with those of related reactions carried out in solution.
Heterolytic Activation of Dihydrogen at Transition‐Metal Sulfur Sites in Coordinatively Unsaturated [rh(L)(“buS4”)]BF4 Complexes, Involving Neutral Hydrides, Thiol Hydrides, and Thiol–Hydride Proton Scrambling (L = CO, PCy3; “buS4”2‐ = 1,2‐Bis[(2‐mercapto‐3,5‐di‐tert‐butylphenylthio]ethane2‐)
Authors: Sellmann Dieter , Rackelmann Gabriele H. , Heinemann Frank W. 
Published: July 2007

Abstract[Rh(H)(L)(“buS4”)] complexes (L = CO (1), PCy3 (2); “buS4”2‐ = 1,2‐bis[(2‐mercapto‐3,5‐di‐tert‐butylphenylthio)ethane2‐]) catalyze the D2/H+ exchange between D2 and EtOH protons in the presence of catalytic amounts of Brønsted acids. A mechanism and complete cycle for the heterolytic D2 cleavage are proposed that are based on characterization of key intermediates and monitoring of key reactions. The key intermediates are the thiol hydride complexes [Rh(H)(L)(“buS4”‐H)]BF4, L = CO (3), PCy3 (4), the coordinatively unsaturated complexes [Rh(L)(“buS4”)]BF4, L = CO (5), PCy3 (6), which are the actual catalysts, and the deuterium‐labeled derivatives of 1–4. Complexes 3 and 4 form from 1 and 2 by protonation with HBF4, and they release H2 to give 5 and 6. Complex 5 dimerizes in the solid state and was characterized by X‐ray structure determination of 5·8CH2Cl2 (triclinic space group P\documentclass{article}\pagestyle{empty}\begin{document}$ \bar 1 $\end{document}, a = 1048.2(4) pm, b = 1430.0(5) pm, c = 1785.7(7) pm, α = 100.49(3)°, β = 102.92(3)°; γ = 103.68(3)°, Z = 1). Complex 6 is mononuclear and adds H2O or THF reversibly to give the highly labile [Rh(L)(PCy3)(“buS4”)]BF4, L = H2O (7), THF (8). CO is irreversibly added to give the stable [Rh(CO)‐(PCy3)(“buS4”)]BF4 (9), whose high‐frequency ν(CO) (2081 cm‐1) indicates a relatively low electron density at the Rh center. Complex 6 also adds to H2 to give 4, which can be deprotonated by solid Na2CO3 or H2O to yield neutral 2. 1H NMR and 2H NMR spectroscopy revealed the scrambling of thiol protons and hydride ligands in 3 and 4 and its deuterium‐labeled derivatives. This exchange of thiol protons for hydride ligands is explained by a transient [Rh(η2‐H2)] species. Low‐temperature 1H/2H NMR spectroscopy showed that protonation of 2 yields four diastereomers of 4 resulting from protonation of the four stereochemically nonequivalent lone pairs at the thiolate donors of 2. The relevance of these findings to H2 activation at transitionmetal sulfur sites in hydrogenases or hydrotreatment catalysts, and differences from the H2 cleavage achieved with other complexes not containing “built‐in” Brønsted‐basic centers, are discussed.
Commentary on ‘Modification of the home environment for the reduction of injuries’, with response from review author
Authors: King W. James 
Published: July 2007

AbstractThis is a commentary on a Cochrane review, published in this issue of EBCH, first published as: Lyons RA, John A, Brophy S, Jones SJ, Johansen A, Kemp A, Lannon S, Patterson J, Rolfe B, Sander LV, Weightman A. Modification of the home environment for the reduction of injuries. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD003600. DOI: 10.1002/14 651 858.CD003600.pub2.Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Characteristics and Key Findings Tables articles. Copyright © 2007 John Wiley & Sons, Ltd.
Written action plans (WAP) for children with asthma: Shoo be do wah or should we do WAP?
Authors: Fitzgerald Dominic A. 
Published: July 2007

AbstractThis is a commentary on a Cochrane review, published in this issue of EBCH, first published as: Bhogal S, Zemek R, Ducharme FM. Written action plans for asthma in children. Cochrane Database of Systematic Reviews 2006, Issue 3. Art. No.: CD005306. DOI: 10.1002/14 651 858.CD005306.pub2.Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Characteristics and Key Findings Tables articles. Copyright © 2007 John Wiley & Sons, Ltd.
Characteristics and key findings for ‘Modification of the home environment for the reduction of injuries’
Authors: van Dalen Elvira , Offringa Martin , Kremer Leontien 
Published: July 2007

AbstractThese are the characteristics and key findings for a Cochrane review, published in this issue of EBCH, first published as: Lyons RA, John A, Brophy S, Jones SJ, Johansen A, Kemp A, Lannon S, Patterson J, Rolfe B, Sander LV, Weightman A. Modification of the home environment for the reduction of injuries. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD003600. DOI: 10.1002/14 651 858.CD003600.pub2.Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Commentary articles. Copyright © 2007 John Wiley & Sons, Ltd.
The Cochrane Library and dietary prevention of allergic disease and food hypersensitivity in children: an umbrella review
Authors: Osborn David A. , Sinn John K. 
Published: July 2007

AbstractBackgroundDietary interventions, including avoiding allergy‐inducing foods in pregnant or lactating women and their infants, and the use dietary modifications such as prebiotics and probiotics, may prevent sensitization and subsequent allergic disease and food hypersensitivity in infants.ObjectivesTo determine the evidence from Cochrane Systematic Reviews for dietary interventions for the primary prevention of clinical allergic disease or food hypersensitivity.MethodsThe Cochrane Database of Systematic Reviews was searched for systematic reviews examining prevention of allergic disease and/or food hypersensitivity. Two reviewers independently assessed review quality, reviewed assessments of study quality and extracted reported data.Main resultsSix reviews were eligible. All reviews had concerns regarding the methodological quality of included studies and several had insufficient numbers of enrolled infants to provide precise estimates of effect. There is insufficient evidence to support the use and safety of maternal dietary allergen restriction during pregnancy and/or lactation for prevention of allergic disease in high‐risk infants. In high‐risk infants unable to be exclusively breast‐fed, there is some evidence for use of a hydrolysed infant formula for prevention of allergic disease, although the evidence is not conclusive. Evidence suggests that soy‐based infant formula should not be recommended. One trial of prebiotic supplemented formula reported a significant reduction in eczema up to 6 months of age. Meta‐analysis of 5 trials of probiotic supplements found a significant reduction in infant eczema, although trial results were heterogeneous.Authors' conclusionsIn high‐risk infants, there is no evidence to support the use of dietary interventions in pregnant or lactating women, or the use of soy‐based formula in infants for prevention of allergic disease. There is insufficient evidence to recommend the use of prebiotics or probiotics. Further trials of hydrolysed infant formula, prebiotics and probiotics are warranted. Copyright © 2007 John Wiley & Sons, Ltd.
Hypoglycemia, brain energetics, and hypoglycemic neuronal death
Authors: Suh Sang Won , Hamby Aaron M. , Swanson Raymond A. 
Published: July 2007

AbstractHypoglycemia is a common and serious problem among diabetic patients receiving treatment with insulin or other glucose‐lowering drugs. Moderate hypoglycemia impairs neurological function, and severe hypoglycemia leads to death of selectively vulnerable neurons. Recent advances have shed new light on the underlying processes that cause neuronal death in hypoglycemia and the factors that may render specific neuronal populations especially vulnerable to hypoglycemia. In addition to its clinical importance, the pathophysiology of hypoglycemia is an indicator of the unique bioenergetic properties of the central nervous system, in particular the metabolic coupling of neuronal and astrocyte metabolism. This review will focus on relationships between bioenergetics and brain dysfunction in hypoglycemia, the neuronal cell death program triggered by hypoglycemia, and the role of astrocytes in these processes. © 2007 Wiley‐Liss, Inc.