bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of Methyl 5′‐Thio‐α‐isomaltoside via an Acyclic Monothioacetal and its Behavior toward Glucoamylase
Authors: Hashimoto Hironobu , Kawanishi Masashi , Yuasa Hideya 
Published: July 2007

AbstractMethyl 5′‐thio‐α‐isomaltoside (1), which contains the ring‐sulfur analogue of the nonreducing glucoside of isomaltose, was synthesized from gentiobiose through a novel ring opening‐recyclization approach. The nonreducing glucoside of per‐O‐benzylated phenyl 1‐thio‐β‐gentiobioside underwent O‐5′–C‐1′ bond cleavage with dimethyl‐boron bromide and thiolacetic acid to give the acyclic monothioacetal 4 with the 1‐thioglucopyranoside at the reducing end intact. The HO‐5′ group in 4 was inverted by a standard oxidation‐reduction process with good efficiency. Recyclization under Mitsunobu condition allowed C‐5′–S‐1′ bond formation with inversion of configuration at C‐5′, to give 1 after functional group interconversion. TLC analysis showed that 1, unlike isomaltose, was not hydrolyzed by glucoamylase from Rhizopus niveus. A fluorometric assay confirmed that the dissociation constant (Kd) for 1 with the enzyme was 39 mM at 20°C, which is comparable with that for isomaltose. A binding assay involving fluorescence titration of the enzyme‐1 complex with gluconolactone indicated that the disaccharide 1 was bound to the catalytic and noncatalytic subsites. Since isomaltose is known to bind only to the noncatalytic subsites, this result indicates a relatively high affinity of the 5‐thioglucose moiety for the catalytic subsite.
[Lithium tert‐butylperoxide]12: Crystal Structure of an Aggregated Oxenoid
Authors: Boche Gernot , Möbus Konrad , Harms Klaus , Lohrenz John C. W. , Marsch Michael 
Published: July 2007

AbstractThe X‐ray crystal structure of the dodecameric lithium tert‐butylperoxide [2]12 is the first of an alkali or alkaline earth peroxide. It shows the lithium ion bridging the two oxygen atoms of the peroxide unit and a slight lenghtening of the O–O bond, in agreement with quantum‐chemical calculations. A calculation for the model reaction of MeLi with LiOOH to give MeOLi and LiOH reveals the importance of Li bridging the O–O bond in the transition state of this reaction, as similarly discussed for many oxidation reactions of (transition‐) metal peroxides. Preliminary theoretical studies of the O–O bond length (and thus of the oxenoid character) as a function of the aggregation of 2 disclose that increasing aggregation leads to stabilization of the charge at the anionic oxygen atom and thus to a reduction of the O–O bond length (oxenoid character). Related considerations of the effect of aggregation should also be valid for other lithium (organometallic) compounds and their structure and reactivity as well as other properties.
Stereoselective Preparation of Polyfunctional Cyclopentane Derivatives by Radical Nickel‐ or Palladium‐Catalyzed Carbozincations
Authors: Stadtmüller Heinz , Vaupel Andrea , Tucker Charles E. , Stüdemann Thomas , Knochel Paul 
Published: July 2007

AbstractThe reaction of 5‐hexenyl iodides with diethylzinc (2 equiv) and catalytic amounts of a PdII or NiII complex like PdCl2(dppf), PdCl2(MeCN)2, or Ni(acac)2 results in an efficient ring closure (THF, RT, 2–12 h) affording cyclopentylmethylzinc iodides, which, after transmetalation with CuCN·2LiCl, can be further functionalized by treatment with a range of electrophiles like allylic halides, acyl chlorides, enones, nitroolefins, ethyl propynoate, and alkynyl halides to yield polyfunctional cyclopentane derivatives. The ring closures occur via radical intermediates, and the stereochemistry of the products can be explained according to the rules for radical cyclizations developed by Beckwith. The preparation of several di‐ and trisubstituted cyclopentanes has been achieved with high stereoselectivity. Tandem ring closures can be performed to construct bicyclic or tricyclic ring systems. Cyclizations of iodo‐ethylenic and acetylenic esters and ketones can be accomplished, although the high reactivity of acetylenic ketones leads to unexpected cyclization products. The synthetic utility of this method has been demonstrated by an enantioselective synthesis of (+)‐methyl epijasmonate and (‐)‐methyl cucurbate.
Gas‐Phase Experiments Aimed at Probing the Existence of the Elusive Water Oxide Molecule
Authors: Schröder Detlef , Schalley Christoph A. , Schwarz Helmut , Goldberg Norman , Hrûsák Jan 
Published: July 2007

AbstractCollisional activation, charge reversal, and six different neutralization ‐ reionization mass spectrometric experiments with [H2,O2]·+ radical cations and [H2,O2]·‐ radical anions were performed in order to probe the predicated existence of neutral water oxide, H2OO, the long sought after tautomer of hydrogen peroxide, HOOH. The experiments together with ab initio calculations indicate that H2OO is a local minimum on the [H2,O2] potential‐energy surface, and the elusive molecule seems to be formed as a transient upon neutralization of the corresponding radical cation H2OO·+ in the gas phase.
Oxidative Degradation of Polychlorinated Phenols Catalyzed by Metallosulfophthalocyanines
Authors: Sorokin Alexander , Meunier Bernard 
Published: July 2007

Abstract2,4,6‐trichlorophenol (TCP) is oxidized by potassium monopersulfate or hydrogen peroxide in the presence of iron or manganese tetrasulfonatophthalocyanines (FePcS or MnPcS) to yield not only the corresponding 2,6‐dichloro‐1,4‐benzoquinone but also ring‐cleavage products. Catalytic oxidation of the TCP ring by hydrogen peroxide is more efficient than by potassium monopersulfate, despite a slower substrate conversion, suggesting that different mechanisms are involved for these two catalytic systems: a metal‐oxo mechanism for FePcS/KHSO5 and a metal‐peroxo mechanism for FePcS/H2O2. Eight different final oxidation products and four quinone intermediates have been identified in the oxidation of TCP by the FePcS/H2O2 catalytic system. Chloromaleic acid is the main product of the oxidative ring cleavage. An iron‐peroxo complex PcS‐FeOOH is probably the active species responsible for the epoxidation of 2,6‐dichloro‐1,4‐benzoquinone and the C–C bond cleavage of 3,5‐dichloro‐2‐hydroxy‐1,4‐benzoquinone ring, both intermediates generated during the catalytic TCP degradation. The oxidation of pentachlorophenol (PCP) is also catalyzed by FePcS or MnPcS with KHSO5 or H2O2.
Novel Heterocumulenes: Bisiminopropadienes and Linear Ketenimines
Authors: Wolf Reinhard , Stadtmüller Stefan , Wong Ming Wah , Wentrup Curt , Barbieux‐Flammang Monique , Flammang Robert 
Published: July 2007

AbstractFlash vacuum thermolysis (FVT) of suitably substituted isoxazol‐5(4H)‐ones 7–9 leads to three different types of ketenimines, namely, the isoxazolonoketenimines 2, the novel bisiminopropadienes RNCCCNR (5), and the C‐cyanoketenimines 14, all characterized by a combination of FVT/matrix isolation/IR spectroscopy and FVT/MS. An unusual, linear CCN‐C backbone in ketenimines 2g and 2h is revealed by their exceptional spectroscopic properties as well as an X‐ray crystal structure of 2g, and confirmed by density functional calculations (B3LYP/6–31 G*); these compounds are best described as resonance hybrids of ketenimines and isonitrile ylides R2C‐CN‐R'. The identification of the highly reactive bisiminopropadienes 5 is supported by the observed shifts in the IR bands of the 15N and 13C isotopomers as well as theoretical calculations, tert‐Butyl‐substituted isoxazolones 7e and 7f, and 8i form the expected ketenimines 2, which then undergo elimination of isobutene and CO2 to generate C‐cyanoketenimines 14 and 14i. N‐Phenyl‐dicyanoketenimine 32 is also described.
Repetitive Strategy for Exponential Growth of Hydroxy‐Functionalized Dendrons
Authors: Klopsch Rainer , Schlüter A.‐Dieter , Franke Peter 
Published: July 2007

AbstractThe synthesis of dendrons with orthogonally protected functional groups, which allows the construction of dendrons in an exponential fashion, is described. The sequence has been carried out on a gram scale for the first, second, and fourth generation. The dendrons have a relatively loose and flexible structure, which should make further growth feasible. Owing to the dendrons' adjustable and broadly applicable substitution pattern, they are the first representatives of a future construction kit for the systematic synthesis of layered dendrimers. The coupling step involves urethane formation.
A General Scheme Based on Empirical Increments for the Prediction of Hydrogen‐Bond Associations of Nucleobases and of Synthetic Host–Guest complexes
Authors: Sartorius Joachim , Schneider Hans‐Jörg 
Published: July 2007

AbstractAssociation energies ΔGt in chloroform, in part also in carbon tetrachloride, were determined by NMR titrations of suitably substituted nucleosides and several synthetic analogues. Based on these and on many literature data, two simple free energy increments were derived describing the ΔGt values of 58 complexes within 1.8 kJ mol‐1. With chloroform as solvent the increment for the primary interaction between donor and acceptor is 7.9 kJ mol‐1, for the secondary one 2.9 kJ mol‐1, irrespective of whether the latter is attractive or repulsive. Addition of only 1% methanol to CCl4 led to a decrease in association constants by a factor of 25. Calorimetric titrations of G‐C nucleoside derivatives in CCl4 showed substantial contributions from G dimers, in line with NMR titrations, and surprisingly small decreases in entropy. Preliminary NOE measurements allowed us to single out some of the possible association modes; they are also in line with expected self‐ and triple‐association modes of the nucleobases. These modes are generally in accord with nucleobase associations predicted by MM calculations in the literature, which in turn agree with predictions based solely on the increments derived in the present work.
Mineralization of Gold Nanoparticles in a Block Copolymer Microemulsion
Authors: Spatz Joachim P. , Mößmer Stefan , Möller Martin 
Published: July 2007

AbstractControlled mineralization of gold nanoparticles has been performed in a microemulsion of polystyrene‐block‐poly(2‐vinylpyridine). The starting point was the formation of a thermodynamically stable dispersion of HAuCl4 in inverse micelles of the block copolymer in toluene, which became metastable when the gold was reduced. Kinetic control of the transformation allowed the following stages of the mineralization/coagulation process to be stabilized: 1) one gold particle per micelle, 2) aggregated micelles containing two or three gold particles, and 3) a state in which empty micelles coexist with larger polymer‐stabilized gold particles. Distinctive variations in the spectra were observed depending on the particle size and whether two particles had formed a couple with orientation‐dependent dipolar interactions.
A Combined Spectroscopic, Photophysical and Theoretical (DFT) Study of the Electronically Excited Inorganometallic Complexes [Ru(E)(E′)(CO)2(iPr–DAB)] (ECl, Me, SnPh3, PbPh3; E′GePh3, SnR3, PbR3 (RMe, Ph); iPr–DAB=N,N'‐diisopropyl‐1,4‐diaza‐1,3‐butadiene): Evidence of an Exceptionally Long‐Lived 3σπ* Excited State for [Ru(SnPh3)2(CO)2(iPr–DAB)]
Authors: Aarnts Maxim P. , Stufkens Derk J. , Wilms Maikel P. , Baerends Evert Jan , Vlček Antonín , Clark Ian P. , George Michael W. , Turner James J. 
Published: July 2007

AbstractThe photophysical properties of the metal–metal bonded complexes [Ru‐(E)(E′)(CO)2(iPr–DAB)] (ECl, E′SnPh3, PbPh3; EMe, E′SnPh3, PbPh3; ESnPh3, E′SnMe3, SnPh3, GePh3; EPbPh3, E′PbMe3, PbPh3, GePh3; iPr–DAB=N,N'‐diisopropyl‐1,4‐diaza‐1,3‐butadiene) have been studied. According to time‐resolved emission, UV/vis and IR spectra, combined with density functional (DFT) MO calculations, the lowest excited state has triplet metal‐to‐ligand charge‐transfer (3MLCT), triplet halide‐to‐ligand charge‐transfer (3XLCT) or 3σ(E–Ru–E)π* character, depending on the nature and combination of the ligands E and E′. The 3σ(E–Ru–E′)π* state is a bound state whose lifetime is strongly influenced by the ligands E and E′. An exceptionally long lifetime (264 μs at 80 K) is observed for the 3σ(Sn–Ru–Sn)π* state of the symmetrically substituted [Ru(SnPh3)2(CO)2(iPr–DAB)] complex. The reason for this long lifetime is the fact that the excited state of this complex is hardly distorted with respect to the ground state, owing to the delocalised character of the σ(Sn–Ru–Sn) bonding orbital, which mixes strongly with the π* orbital of the iPr–DAB ligand. This delocalisation is also responsible for the unusually high oscillator strength of the σ → π* electronic transition in the visible spectral region.
Molecular Recognition by Hydrogen Bonding in Polyelectrolyte Multilayers
Authors: Laschewsky André , Wischerhoff Erik , Denzinger Steffen , Ringsdorf Helmut , Delcorte Arnaud , Bertrand Patrick 
Published: July 2007

AbstractFunctional polyanions were prepared by copolymerization of sulfopropyl acrylate and sulfopropyl methacrylate with monomers bearing triaminopyrimidine or barbituric acid functionalities, respectively. Functionalized polyelectrolyte multilayers were assembled from these copolymers by stepwise alternating adsorption with poly(choline methacrylate). These multilayers are suited for molecular recognition of substrates that are complementary to the functional groups incorporated. Thus, multilayers containing triaminopyrimidine moieties selectively bind barbituric acid, and vice versa, when exposed to solutions of the 1:1 complex of barbituric acid and triaminopyrimidine. The molecular recognition process was monitored by UV/Vis spectroscopy, time‐of‐flight secondary ion mass spectroscopy (ToF‐SIMS), and photoelectron spectroscopy (XPS). Remarkably, after successful recognition and binding of the complementary substrates to the multilayers, the stepwise layering could be continued.
Total syntheses of the slime mold alkaloid arcyriacyanin A
Authors: Brenner Michael , Mayer Guido , Terpin Andreas , Steglich Wolfgang 
Published: July 2007

AbstractArcyriacyanin A (1) has been synthesized by three different routes. In the first synthesis the bisbromomagnesium salt of 2,4′‐biindole (5) was treated with dibromomaleimide (6) to yield arcyriacyanin A (1). The second approach used an intramolecular Heck reaction for the cyclization of a 4‐(triflyloxy)arcyriarubin 8 to N‐methylarcyriacyanin A (2). Thirdly, compound 2 was obtained by a domino Heck reaction between 3‐bromo‐4‐[1‐(tert‐butoxycarbonyl)indol‐3‐yl]‐1‐methylmaleimide (9) and 4‐bromoindole (10). The N‐methyl derivative 2 could be transformed into arcyriacyanin A (1) by standard methods.
The Oxide Anion Accelerated Retro‐Diels‐Alder Reaction
Authors: Bunnage Mark E. , Nicolaou K. C. 
Published: July 2007

AbstractThe widespread application of the retro‐Diels‐Alder reaction in synthesis has been hampered by the high temperatures usually required to effect cycloreversion. The discovery of the anionic oxy‐Cope reaction was followed by predictions that the accelerating effect of the oxide anion should also be observed with other pericyclic reactions. Recently, such predictions have been confirmed for the retro‐Diels‐Alder reaction, which often proceeds rapidly at room temperature by oxide anion rate acceleration. Such mild retro‐Diels‐Alder reactions have now been employed in the synthesis of a range of molecular targets, including temperature‐sensitive enediynes.
Heterosupramolecular Chemistry: Self‐Assembly of an Electron Donor (TiO2 Nanocrystallite)‐Acceptor (Viologen) Complex
Authors: Cusack Lucy , Rao S. Nagaraja , Fitzmaurice Donald 
Published: July 2007

AbstractA TiO2 nanocrystallite has been modified to recognise and selectively bind, by complementary hydrogen bonding, a uracil substrate incorporating a viologen moiety. Band‐gap excitation of the self‐assembled donor (TiO2 nanocrystallite)‐acceptor (viologen) complex results in electron transfer. Some implications of these findings for the self‐assembly of functional nanostructures containing both condensed phase and molecular components are considered.
Hexabromotricyclobutabenzene and Hexabromohexaradialene: Their Nickel‐Mediated One‐Pot Syntheses and Crystal Structure
Authors: Stanger Amnon , Ashkenazi Nissan , Boese Roland , Bläser Dieter , Stellberg Peter 
Published: July 2007

AbstractThe reaction of hexakis(dibromomethyl)benzene with [(Bu3P)2‐Ni(COD)] (COD = 1,5‐cyclooctadiene) in DMF at 65–70°C yielded a mixture of the title compounds. The mixture was separated by column chromatography to yield hexabromotricyclobutabenzene (3 a) and hexabromohexaradialene (4) in 24 and 16% yields, respectively. 1H and 13C NMR spectroscopy suggest that 3 is obtained as the syn‐all‐trans isomer 3 a, and the symmetric anti‐all‐trans isomer 3 b is not obtained at all. The X‐ray structures of 3 a and 4 are reported. The hexaradialene 4 has a chair conformation, and deviates from planarity by 43.6°. Heat or radical impurities cause the clean transformation of 3 a to 4.
Terrylenimides: New NIR Fluorescent Dyes
Authors: Holtrup Frank O. , R. J. Müller Gert , Quante Heribert , De Feyter Steven , De Schryver Frans C. , Müllen Klaus 
Published: July 2007

AbstractTerrylenimides 3 and 4 represent a new class of blue colorants, exhibiting absorption maxima at 650 to 700 nm and fluorescence emissions in the NIR region (673 to 750 nm). The terrylenimides were synthesized by means of various organometallic coupling reactions, catalyzed by transition metal complexes (Nio, Pdo) and starting from the aromatic bromides, boronic acids, or organotin compounds. The terrylenimides have all the properties expected of excellent fluorescent dyes: high extinction coefficients, high fluorescence quantum yields, and very good thermal, chemical, and photochemical stabilities. Owing to its extended π system, 3 can reversibly accept four negative charges. By varying the substituents, 3 and 4 can be modified to serve either as soluble dyes or as insoluble pigments.
Evidence for DirecttransInsertion in a Hydrido‐Olefin Rhodium Complex—Free Nitrogen as a Trap in a Migratory Insertion Process
Authors: Vigalok Arkadi , Kraatz Heinz‐Bernhard , Konstantinovsky Leonid , Milstein David 
Published: July 2007

AbstractReduction of the hydrido chloride complex [Rh(H)Cl{CH3C(CH2CH2‐P(tBu)2)2}] (4) with NaH under a nitrogen atmosphere results in formation of two products: the dinitrogen complex [Rh(N2)‐{CH3C(CH2P(tBu)2)2}](2)and the unusual low‐valent hydrido‐olefin complex, [RhH{CH2C(CH2CH2P(tBu)2)2}](3). In the presence of N2, complexes2and3are in equilibrium in solution;2is about 2.9kcalmol−1more stable than3+ N2. Both complexes co‐crystallize in the solid state; they occupy the same crystallographic site in the crystal lattice (P2‐(1)/c;Z= 4;a= 12.173(2),b= 14.121 (3),c= 15.367 (3); α = 90, β = 106.50(3), γ = 90°). The mechanism of the reversible interconversion of2and3has been studied in detail. Complex3undergoes rapid olefin insertion/β‐hydrogen elimination processes. The insertion rates were measured at different temperatures by saturation transfer NMR experiments, providing evidence for a highly organized late transition state (δS≠≈︂ – 40 e.u.), which can be caused by a concerted “transmigration”. This theoretically unfavorable process is assisted by a distortion from the ideal square‐planar configuration, including a decrease of the P‐Rh‐P angle and some bias of the double bond toward the hydride as indicated by the X‐ray crystal structure of3. Under a nitrogen atmosphere, the intermediate formed upon olefin insertion is slowly trapped by free dinitrogen to form complex2. The dinitrogen dissociation from2was found to be the rate‐determining step for the overall interconversion of2and3(δG≠298= 24.1 kcalmol−1).
Nickel Complexes of 21‐Oxaporphyrin and 21, 23‐Dioxaporphyrin
Authors: Chmielewski Piotr J. , Latos‐Grażyński Lechoslaw , Olmstead Marilyn M. , Balch Alan L. 
Published: July 2007

AbstractThe nickel(I) and nickel(II) complexes of 5,20‐bis(p‐tolyl)‐10, 15‐diphenyl‐21‐oxaporphyrin (ODTDPPH) and 5,10,15,20‐tetraphenyl‐21, 23‐dioxaporphyrin (O2TPP) have been investigated. These oxa analogues of 5,10,15,20‐tetraarylporphyrin, where one or two pyrrole rings are replaced by a furan moiety, have been synthesized by condensation of the respective precursors, namely 2,5‐bis(arylhydroxymethyl)furan, pyrrole, and arylaldehyde. Insertion of nickel(II) into ODTDPPH or O2TPP yielded high‐spin five‐ and six‐coordinate ([(ODTDPP)NiIICl] and [(O2TPP)NiIICl2]) complexes, which can be reduced with moderate reducing reagents. The EPR spectra of [(ODTDPP)NiI] and [(O2TPP)NiICl] revealed the NiI oxa(dioxa)porphyrin rather than a NiI anion radical electronic structure. In the structures of [(ODTDPP)NiIICl], [(O2TPP)NiIICl2], and [(ODTDPP)NiI], determined by X‐ray diffraction, the furan ring is planar and coordinates in the η1 fashion through the trigonal oxygen atom; the nickel ion lies in the furan plane for the latter two complexes, but slightly outside it in [(ODTDPP)NiIICl]. The Ni–N and Ni–O bond lengths decrease upon reduction of high‐spin five‐coordinate [(ODTDPP)NiIICl] to four‐coordinate [(ODTDPP)NiI]. The pattern of downfield pyrrole resonances in 1H NMR spectra of [(ODTDPP)NiIICl] and [(O2TPP)‐NiIICl2] has been established. The downfield positions of furan resonances are unusual for NiII heteroporphyrins; they have been accounted for by the nearly in‐plane coordination of the furan moiety as opposed to the side‐on coordination found for thiophene‐ or selenophene‐containing heteroporphyrins. An example of ion‐pair formation, [(O2TPPH)2][NiIICl4], was produced from [(O2TPP)NiIICl2] by acidification with HCl.
New Aspects of the Photophysical Properties of 1′H‐2′,3′‐Dimethoxycarbonylspiro[fluoren‐9,1′‐pyrrolo[2,1‐a]quinoline]
Authors: Andreis Christine , Dürr Heinz , Wintgens Véronique , Valat Pierre , Kossanyi Jean 
Published: July 2007

AbstractIn this paper we describe photophysical and mechanistic studies of spiro[fluorene‐9,1′‐pyrrolo[2,1‐a]quinolines] (DHI) 1–4 and of their styryl homologues 5–11 (styryl DHI). DHIs 1–11 have low fluorescence quantum yields (approximately ϕf = 10‐3). The position of the fluorescence emission band is temperature‐dependent. The ring‐opened betaines 1′–11′ do not fluoresce at all. DHIs 1–11 exhibit phosphorescence, which is hypsochromically shifted by NO2 substitution of the fluorene ring. The triplet can be populated only by sensitization (with benzophenone as sensitizer) and, therefore, the reaction that occurs under direct excitation of the molecule involves the singlet excited state only. On irradiation under time‐resolved conditions, two transients were seen to be formed in the picosecond and microsecond domains. Slightly tilted educt or product‐like geometries are attributed to these transients. An energy diagram is proposed for the photoreaction of the model compound spiro[pyrroloquinoline] 1 → 1′, which takes into account the singlet pathway and the different transients of ca. 100 ps lifetimes formed from the singlet excited state of 1–11.