bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modification of (1R,2S)‐1,2‐Diphenyl‐2‐aminoethanol for the Highly Enantioselective, Asymmetric Alkylation of N‐Diphenylphosphinoyl Arylimines with Dialkylzinc
Authors: Zhang Hai‐Le , Jiang Fan , Zhang Xiao‐Mei , Cui Xin , Gong Liu‐Zhu , Mi Ai‐Qiao , Jiang Yao‐Zhong , Wu Yun‐Dong 
Published: March 2004

AbstractExperimental studies on the modification of (1R,2S)‐1,2‐diphenyl‐2‐aminoethanol, which is used to promote the alkylation of N‐diphenylphosphinoyl benzalimine with diethylzinc, revealed that N‐monosubstituted amino alcohols exhibited higher enantioselectivities than their N,N‐disubstituted counterparts and imino alcohols. Application of the optimal chiral ligand 3 c to activate the reaction of N‐diphenylphosphinoyl arylimines with diethylzinc and dibutylzinc resulted in excellent enantiomeric selectivities of up to 98 % ee. The origin of the experimentally observed enantioselectivities was revealed by density functional calculations (B3LYP/6‐31G*) on the transition structures of several model reactions.
Heck Coupling Reaction of Iodobenzene and Styrene Using Supercritical Water in the Absence of a Catalyst
Authors: Zhang Rong , Sato Osamu , Zhao Fengyu , Sato Masahiro , Ikushima Yutaka 
Published: March 2004

AbstractHeck coupling reaction of iodobenzene and styrene proceeds rapidly and selectively in supercritical water even without any catalyst in the presence of base. Both the choice of base and the reaction conditions had a significant effect on the conversion and the selectivity of the coupling products. The addition of a relatively mild base such as potassium acetate facilitated the cross‐coupling reaction, while the hydrolysis of phenyl halide was favored in the presence of a strong base. The conversion and the yields of coupling products increased with increasing temperature, reaching a maximum at 650 K near the critical temperature of water, and then decreased as the temperature was further increased. Water density had a significant influence on the reaction rate, showing nearly 30 % augmentation with a slight increase in density from 0.45 to 0.56 g cm−3, but had less effect on the product selectivity. Two possibilities of the role of water responsible for the noncatalytic Heck coupling reaction in supercritical water, that is, ion and water‐catalyzed mechanisms have been considered.
Blowup in a three‐dimensional vector model for the Euler equations
Authors: Friedlander Susan , Pavlović Nataša 
Published: March 2004

AbstractWe present a three‐dimensional vector model given in terms of an infinite system of nonlinearly coupled ordinary differential equations. This model has structural similarities with the Euler equations for incompressible, inviscid fluid flows. It mimics certain important properties of the Euler equations, namely, conservation of energy and divergence‐free velocity. It is proven for certain families of initial data that the model system permits local existence in time for initial conditions in Sobolev spaces Hs, s > $5 \over 2$; and blowup occurs in the sense that the H3/2 + ϵ norm becomes unbounded in finite time. © 2004 Wiley Periodicals, Inc.
Oscillation and convergence behaviours exhibited in an ‘unstable’ second‐order digital filter with saturation‐type non‐linearity
Authors: Ling Bingo Wing‐Kuen , Ho Charlotte Yuk‐Fan , Leung Raymond Shing‐Keung , Tam Peter Kwong‐Shun 
Published: March 2004

AbstractThis letter explains the oscillatory behaviours exhibited in a second‐order digital filter with saturation‐type non‐linearity via the Hopf bifurcation theorem. It is shown that depending on the bifurcation parameter, the state variables may converge to zero even when the eigenvalues of the system matrix are outside the unit circle. Copyright © 2004 John Wiley & Sons, Ltd. abstract
Autonomous response of a third‐order digital filter with two's complement arithmetic realized in cascade form
Authors: Ling Bingo Wing‐Kuen , Hung Wai‐Fung , Tam Peter Kwong‐Shun 
Published: March 2004

AbstractIn this letter, results on the autonomous response of a third‐order digital filter with two's complement arithmetic realized as a first‐order subsystem cascaded by a second‐order subsystem are reported. The behaviour of the second‐order subsystem depends on the pole location and the initial condition of the first‐order subsystem, because the transient behaviour is affected by the first‐order subsystem and this transient response can be viewed as an excitation of the original initial state to another state. New results on the set of necessary and sufficient conditions relating the trajectory equations, the behaviours of the symbolic sequences and the sets of the initial conditions are derived. The effects of the pole location and the initial condition of first‐order subsystem on the overall system are discussed. Some interesting differences between the autonomous response of the second‐order subsystem and the response due to the exponentially decaying input are reported. Some simulation results are given to illustrate the analytical results. Copyright © 2004 John Wiley & Sons, Ltd.
On dissipative two‐state quantum cells and cellular networks
Authors: Civalleri Pier Paolo , Gilli Marco 
Published: March 2004

AbstractQuantum cellular networks are structures composed of two‐state quantum cells in equilibrium with a stationary thermal bath, which interact among themselves in a classical way. It is shown that if system–bath coupling is set up in the representation based on the given states, as done in the literature, or in the energy representation, as the theory assumes under several approximations, different models are obtained for the cell performance, and hence for the dynamics of the whole network. The model based on the state representation could also be derived by a heuristic approach. The final choice should be decided by experiment. Copyright © 2004 John Wiley & Sons, Ltd.
The role of pdx1 and HNF6 in proliferation and differentiation of endocrine precursors
Authors: Wilding Laura , Gannon Maureen 
Published: March 2004

AbstractEx vivo expansion of embryonic stem cells (ES cells) or pancreatic stem cells for insulin delivery to diabetic patients provides potential for the restoration of islet function in these individuals. Understanding the spatial and temporal requirements of crucial factors for endocrine progenitor specification, proliferation, and terminal differentiation remains a major challenge in the field of pancreas development. Here, we provide speculation as to the role of pdx1 and HNF6 in these different stages of pancreatic endocrine cell development. At the time when islets begin to form within the pancreas, the expression patterns of pdx1 and HNF6 diverge, suggesting distinct functions for each of the genes over the course of endocrine cell development. The current body of evidence provides support for a role of both factors in early endocrine specification as well as a requirement for pdx1 in the generation of mature pancreatic endocrine cells. The precise temporal requirement of HNF6 in the production of terminally differentiated endocrine cells remains unclear. Future studies in this area will rely on conditionally manipulatable systems in combination with lineage‐tracing studies for a more accurate assessment of pdx1 and HNF6 function at different stages along the pathway of endocrine cell development. Copyright © 2004 John Wiley & Sons, Ltd.
Current literature in diabetes
Authors:   John Wiley & Sons, Ltd.
Published: March 2004

AbstractIn order to keep subscribers up‐to‐date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of diabetes/metabolism. Each bibliography is divided into 17 sections: 1 Books, Reviews & Symposia; 2 General; 3 Genetics; 4 Epidemiology; 5 Immunology; 6 Prediction; 7 Prevention; 8 Intervention: a) General; b) Pharmacology; 9 Pathology: a) General; b) Cardiovascular; c) Neurological; d) Renal; 10 Endocrinology & Metabolism; 11 Nutrition; 12 Animal Studies; 13 Techniques. Within each section, articles are listed in alphabetical order with respect to author (6 Weeks journals ‐ Search completed at 21st Jan. 2004)
High‐frequency C‐V characteristics of a buried‐channel MOS capacitor
Authors: Miyake Masayasu 
Published: March 2004

AbstractThis paper discusses the high‐frequency equilibrium‐state capacitance–voltage (C–V) characteristics of a buried‐channel MOS capacitor, that is, a MOS capacitor with a thin p‐type layer at the surface of an n‐type Si substrate. For this device, changing the gate voltage in the negative direction converts the surface p‐type layer from a depletion region into an accumulation region (an inversion region for the n‐type substrate). The high‐frequency characteristics reveal that the capacitance first decreases to a minimum and then saturates after a slight increase. The author discusses the underlying physics of this capacitance minimum, which is a peculiar characteristic of buried‐channel MOS capacitors, based on the general relation between the high‐frequency capacitance and the depletion layer width. The discussion suggests that the origin of this effect is an ac component of the density distribution of holes that follows the high‐frequency signal, even when the total number of holes is unable to track the same signal. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(4): 25–33, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10081
An architecture for realizing a distributed voice conference system over IP networks
Authors: Yamada Hideaki , Oda Toshikane 
Published: March 2004

AbstractWith the rapidly spreading use of IP networks such as intranets and the Internet, there have been efforts to develop voice‐over IP (VoIP) devices and services by utilizing them. In particular, in the commercial user environment, wide use is likely to be made of services with a high added value in which the telephone network function and the IP network connection function are combined by fully utilizing a high‐level user interface provided by an information processing terminal. This paper considers a voice conference service as the value‐added service in which the telephone function terminals on the telephone network and IP network are interconnected. The construction of a system for providing a voice conference service is investigated, considering requirements such as flexibility, scalability, and quality. A method of construction is proposed. The effectiveness of the proposed method is demonstrated by performance evaluation of an experimental system based on the method. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(4): 53–64, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20071
An Alternative Procedure for the Synthesis of [5]‐ and [7]Carbohelicenes
Authors: El Abed Riadh , Ben Hassine Béchir , Genêt Jean‐Pierre , Gorsane Mohamed , Marinetti Angela 
Published: March 2004

Abstract2‐Bromo[5]helicene derivatives and substituted [7]helicenes have been prepared through a synthetic sequence relying on Heck‐type and photocyclodehydrogenation reactions. This procedure provides a new, versatile and efficient approach to helicene derivatives. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Electron‐Transfer Cycloreversion of 2,3‐Diaryloxetanes: Influence of the Substitution and the Photosensitizer on the Regioselectivity
Authors: Izquierdo M. Angeles , Miranda Miguel A. 
Published: March 2004

AbstractThe regioselectivity in the oxidative electron‐transfer cycloreversion (CR) of 2,3‐diaryloxetanes depends on the substitution of the aryl groups and on the nature of the electron‐transfer photosensitizer. The reaction occurs with fragmentation of the C2−C3 and C4−O bonds either in the presence of electron‐releasing substituents in the 3‐aryl groups, or when chloranil is used as photosensitizer. Thus, CR of the methoxy‐substituted derivative trans,trans‐3‐(4‐methoxyphenyl)‐4‐methyl‐2‐phenyloxetane (1b) results in the production of trans‐anethole and benzaldehyde. In this case, the trans‐anethole radical cation has been detected as transient intermediate by means of laser flash photolysis. Likewise, CR of 1a, photosensitized by chloranil, results in the formation of products arising from the trapping of the trans‐β‐methylstyrene radical cation by chloranil‐derived intermediates. The reverse regioselectivity has been previously found in the ET cycloreversion of 4‐methyl‐2,3‐diphenyloxetane (1a) using (thio)pyrylium salts as photosensitizers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of Aliphatic (E)‐α,β‐Unsaturated Amides with High Diastereoselectivity from α,β‐Epoxyamides Promoted by SmI2/HMPA
Authors: Concellón José M. , Bardales Eva 
Published: March 2004

AbstractSynthesis of aliphatic (E)‐α,β‐unsaturated amides 2, in which the C=C bond is di‐ or trisubstituted, is achieved by using samarium diiodide and HMPA. The starting compounds 1 were easily prepared by the reaction of the corresponding lithium or potassium enolates of α‐chloroamides with aldehydes. A mechanism to explain this process is proposed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Captodative Stabilization in Geminally Substituted Allylic Radicals Assessed by Means of the EPR‐Spectral D Parameter of 1,3‐Cyclopentanediyl Triplet Diradicals
Authors: Adam Waldemar , Schulte Claudio M. Ortega 
Published: March 2004

AbstractThe EPR‐spectral zero‐field parameter D of low‐temperature persistent triplet diradicals T was used to assess the electronic substituent effects in EA/ED and ED/ED geminally substituted allylic radicals. From these EPR data, the interaction parameter (ΔS) was calculated for a set of doubly functionalized radicals, which expresses the ability of the unpaired electron to interact either individually with the functional groups or simultaneously in either a synergistic or antagonistic way. We show that the ED/ED combinations interact antagonistically with the odd electron, whereas the R2N/EA and the MeO/EA pairs display a pronounced captodative delocalization. Compared to MeO/EA, the MeS/EA functionalities manifest just an additive effect of the individual substituents. These results are rationalized in terms of appropriate electron‐transfer‐type mesomeric structures. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of Enantiopure 1‐Aryl‐1‐butylamines and 1‐Aryl‐3‐butenylamines by Diastereoselective Addition of Allylzinc Bromide to Imines Derived from (R)‐Phenylglycine Amide
Authors: Dalmolen Jan , van der Sluis Marcel , Nieuwenhuijzen José W. , Meetsma Auke , de Lange Ben , Kaptein Bernard , Kellogg Richard M. , Broxterman Quirinus B. 
Published: March 2004

AbstractThe synthesis of enantiopure 1‐aryl‐1‐butylamines via a highly diastereoselective addition of allylzinc bromide to imines derived from (R)‐phenylglycine amide is reported. These are synthesised by a three‐step procedure, which involves: (a) formation of the chiral imines; (b) asymmetric addition of the allylzinc reagent; (c) removal of the chiral auxiliary by means of a reductive or non‐reductive method. The reductive method provides 1‐aryl‐1‐butylamines whereas the non‐reductive method preserves the double bond to afford 1‐aryl‐3‐butenylamines. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Reciprocal Donor Acceptor Selectivity (RDAS) and Paulsen’s Concept of “Match” in Saccharide Coupling
Authors: Fraser‐Reid Bert , López J. Cristóbal , Gómez Ana M. , Uriel Clara 
Published: March 2004

AbstractThree modes of selectivity — enantio, stereo, and regio — are critically important for efficient organic synthesis. In the sub‐domain of oligosaccharide synthesis, the first is (usually!) irrelevant in view of the chiralities of the reacting partners. The challenge posed by the other two is compounded by the reality that “protecting groups” are the major, if not only, instruments by which control can be exercised. The role that O2 protecting groups play in stereocontrol of coupling reactions was formulated 60 years ago. In this microreview, evidence is presented which shows that O2 protecting groups also exercise regiocontrol. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Efficient Synthesis of Structurally Diverse Diazabicycloalkanes: Scaffolds for Modular Dipeptide Mimetics with Tunable Backbone Conformations
Authors: Maison Wolfgang , Grohs Daniel C. , Prenzel Alexander H. G. P. 
Published: March 2004

AbstractA stereoselective synthesis of new dipeptide mimetics based on a diazabicycloalkane scaffold is reported. The route starts from enantiomerically pure azabicycloalkenes 1 that are bis(hydroxylated) and coupled N‐terminally to a second amino acid. The key step of the reaction sequence is an oxidative cleavage of the resulting dipeptides 5 to give highly functionalised diazabicycloalkanes 6, which can be easily converted into a number of dipeptide mimetics with defined and variable stereochemistry and a number of different amino acid side chains. The backbone dihedral angles within these dipeptide mimetics can be tuned by varying the stereochemistry and the ring sizes of the diazabicycloalkane scaffold. The syntheses of conformationally constrained dipeptide analogues in four to five steps are presented. With the syntheses of dipeptide mimetics 19a−c, suitable linker moieties for conjugation of diazabicycloalkanes to other functional molecules like markers or solid phases are introduced, making these compounds modular dipeptide mimetics that might find applications as modular ligands or as solid‐phase‐attached scaffolds in combinatorial chemistry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Photoinduced Electron‐Transfer, Pyrolyses, and Direct Irradiation Reactions of 2‐Methylenecyclobutanones: Regioselective Bond Cleavage Depends on the Substituents and the Method of Activation
Authors: Ikeda Hiroshi , Tanaka Futoshi , Miyashi Tsutomu , Akiyama Kimio , Tero‐Kubota Shozo 
Published: March 2004

AbstractThe regioselectivity of bond cleavage and the subsequent reactivity of 4‐methylene‐3,3‐dimethyl‐2,2‐diphenylcyclobutan‐1‐one (5) and 4‐isopropylidene‐2,2‐diphenylcyclobutan‐1‐one (6) in photoinduced electron transfer, pyrolysis, and direct irradiation reactions were investigated. Novel photoinduced electron‐transfer rearrangements of 5 and 6 were found to occur through 1,4‐diyl radical cations formed by C1−C2 cleavage of 5·+ and 6·+; that is, similarly to radical‐cation Norrish type I cleavage, but in contrast to the diansyl derivative 1·+ corresponding to 5·+, which gives an oxatetramethyleneethane (OTME)‐type radical cation through C2−C3 cleavage. In contrast, solvent effects on the thermal rearrangement of 5 to 6 and theoretical calculations suggested the intervention of an OTME‐type diradical intermediate 16·· formed by homolytic C2−C3 cleavage of 5. In direct photoreactions, 5 and 6 undergo [2+2] cycloreversion to give 1,1‐diphenylethylenes and methyleneallenes, which are explained by both C1−C2 and C3−C4 cleavage. Consequently, the regioselectivity of 5 and 6 in bond cleavage and their reactivity strongly depend on the substituents and the method of activation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Effect of Substituents on the Complexation of Aromatic and Quinoid Substrates with Molecular Tweezers and Clips
Authors: Klärner Frank‐Gerrit , Polkowska Jolanta , Panitzky Jens , Seelbach Uta P. , Burkert Ulrich , Kamieth Markus , Baumann Michael , Wigger Arne E. , Boese Roland , Bläser Dieter 
Published: March 2004

AbstractMolecular tweezers and clips of type 1−3 substituted with OAc, OH, OCONHPh, OMe, OCH2COOR and OCH2CONHR groups in the central spacer units have been synthesized by modification, by standard methods, either of the known diacetoxy‐substituted derivatives 1b, 2b and 3b, or of the correspondingly substituted bis‐dienophiles 4b and 5b. The synthesis of the dimethoxy‐diacetoxy‐substituted tweezer 1d could be accomplished through pressure‐induced repetitive Diels−Alder reactions between the bis‐dienophile 4b and the newly prepared diene 6b and subsequent DDQ oxidation. The thermodynamic parameters (Ka and ΔG) of complex formation between the new receptors and aromatic substrates such as DCNB 21, TCNB 22, TCNQ 24 and Kosower salt 25 and the maximum complexation‐induced 1H NMR shifts (Δδmax.) were determined by 1H NMR titration experiments. It was found that the presence of substituents OH, OAc and OCONHPh in the central spacer units of the tweezers and clips 1−3 favours complex formation, whereas that of the substituents OMe, OCH2COOR and OCH2CONHR disfavours it. This finding can be explained in terms of the size and different conformations of these groups in the tweezer and clip molecules as calculated by force‐field (MMFF) techniques rather than of their influence on the electrostatic potential surfaces (EPSs) of the adjacent aromatic rings as calculated by quantum mechanical methods. The complementary natures of the negative EPSs inside the tweezer and clip cavities and the positive EPSs of the substrates forming complexes explained the high selectivity of these receptors toward electron‐deficient substrates. The finding that the self‐assembly of the OCH2COOCH2CH3 side chain is only observed for the benzene‐spaced tweezers 1i and 1o confirms earlier results obtained for the intermolecular complexation of these receptors. Accordingly, the benzene‐spaced tweezers of type 1 selectively bind aliphatic substrates, whereas the naphthalene‐spaced tweezers of type 2 and clips of type 3 preferentially complex aromatic substrates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Asymmetric Synthesis of Cycloalkenyl and Alkenyloxiranes From Allylic Sulfoximines and Aldehydes and Application to Solid‐Phase Synthesis
Authors: Gais Hans‐Joachim , Babu Gadamsetti S. , Günter Markus , Das Parthasarathi 
Published: March 2004

AbstractAn asymmetric synthesis of cycloalkenyl and alkenyloxiranes from allylic sulfoximines and aldehydes is described. Lithiation and titanation of cyclic and acyclic allylic sulfoximines with chlorotris(diethylamino)titanium and subsequent treatment with aldehydes gave, as described previously, enantio‐ and diastereomerically pure, syn‐configured, sulfoximine‐substituted homoallylic alcohols. Treatment of the sulfoximine‐substituted homoallylic alcohols with chloroethyl chloroformate resulted in a facile substitution of the sulfoximine group by a Cl atom, with formation of the corresponding alkenyl chlorohydrins. In the case of the cycloalkenyl derivatives the substitution proceeded with high diastereoselectivities with retention of configuration, while in the case of the alkenyl derivatives, medium diastereoselectivities with inversion of configuration were observed. While elimination reactions of the cycloalkenyl chlorohydrins gave the corresponding enantio‐ and diastereomerically pure cis‐configured cycloalkenyloxiranes in good overall yields, the alkenyl chlorohydrins afforded mixtures of enantiomerically pure trans and cis isomers in which the trans isomers dominated. The solution‐phase synthesis was extended to the solid phase by the synthesis of an enantiomerically pure, polymer‐bound allylic sulfoximine and its conversion into an alkenyloxirane. The initial results proved that the concept of the utilization of the sulfoximine group as a traceless chiral linker is feasible and suggest that the solid‐phase asymmetric synthesis of cycloalkenyloxiranes by this route should be possible. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)