bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radical Cyclization Reactions
Authors: Giese B. , Kopping B. , Göbel T. , Dickhaut J. , Thoma G. , Kulicke K.J. , Trach F. 
Published: April 2004

AbstractRadical cyclization reactions are among the most powerful and versatile methods for the construction of mono‐ and polycyclic systems. The advantages these reactions offer to the synthetic organic chemist include high functional group tolerance and mild reaction conditions combined with high levels of regio‐ and stereochemistry. Furthermore, the recent progress in radical chemistry has led to the development of a broad range of very useful practical methods to conduct radical cyclization reactions. In general, radical cyclization reactions comprise three basic steps: selective radical generation, radical cyclization, and conversion of the cyclized radical to the product.For the generation of the initial radical a broad variety of suitable precursors can be employed, such as halides, thio‐ and selenoethers, alcohols, aldehydes and hydrocarbons. The cyclization step usually involves the intramolecular addition of a radical to a multiple bond. Most often carbon–carbon multiple bonds are employed; however, there are also examples known for the addition to carbon–oxygen and carbon–nitrogen bonds. Depending on the method employed, the cyclized radical is converted to the desired product by trapping with a radical scavenger, by a fragmentation reaction, or by an electron transfer reaction.The section Mechanism, Regio‐ and Stereochemistry provides an introduction to the key features of radical cyclization with a special emphasis on the factors controlling the regio‐ and stereochemistry. The section Scope and Limitations covers the different methods used to conduct radical cyclization. The basic principles of radical chemistry and general practical considerations when conducting radical cyclizations are not discussed in detail. Several excellent review articles and books dealing with these topics are available.
Oxidation of Carbonyl Compounds with Organohypervalent Iodine Reagents
Authors: Moriarty Robert M. , Om Prakash  
Published: April 2004

AbstractThe search for novel oxidizing agents, especially those that not only transform a broad range of diverse functional groups, but also do so with a high degree of selectivity, remains the focus of intense exploration. In recent years, the use of hypervalent iodine compounds as oxidizing agents has gained attention in synthetic organic chemistry. The α‐oxidation of carbonyl compounds by hypervalent iodine oxidants has been most widely investigated and has broad synthetic utility. Although this area has recently been reviewed in various forms and scope, a comprehensive coverage that focuses on synthetic applications is absent and the present chapter addresses this need.In this chapter the oxidation of carbonyl compounds with hypervalent iodine reagents is discussed. These reagents effect the electrophilic α‐oxidation of large numbers of ketones, β‐diketones, α,β‐unsaturated ketones, and their derivatives such as silyl enol ethers. The discussion is restricted mainly to the reactions of organoiodine(III) reagents; inclusion of other hypervalent iodine reagents such as organoiodine(V) reagents, periodic acid, or purely inorganic iodate reagents is beyond the scope of this chapter. Furthermore, reactions brought about with other oxidizing agents in combination with a catalytic amount of a hypervalent iodine reagent are not considered here. The chapter also excludes discussion of a considerable amount of work based upon the reaction of iodonium ylides, a distinct feature of organoiodine(III) reagents. The common abbreviations and names of the reagents used in this chapter are listed.A general feature of the reactions of carbonyl compounds described in this chapter is electrophilic attack of the organoiodine(III) reagent at the α‐carbon atom of a carbonyl group to yield a presumed tricoordinate iodine(III) intermediate.The Intermediate reacts further to yield products via various pathways depending upon the reaction conditions. The major processes that occur are summarized. These include oxidation of ketones under basic conditions leading to α‐hydroxydimethylacetals, oxidation of α,β‐unsaturated ketones leading to α‐hydroxy‐β‐methoxydimethylacetals, oxidation of ketones under neutral conditions, and related oxidation of silyl enol ethers under various conditions leading to α‐functionalization, intramolecular participation reactions leading to oxygen‐containing heterocyclic compounds including cyclic α‐keto ethers and lactones, and rearrangement processes such as 1,2‐aryl shifts in alkyl aryl ketones leading to 2‐arylalkanoates. All of these reactions are driven by the reduction of iodine(III) to iodine(I) (iodobenzene).
Synthetic Uses of Tosylmethyl Isocyanide (TosMIC)
Authors: Leusen Daan Van , Leusen Albert M. Van 
Published: April 2004

AbstractTosMIC is the acronym for 4‐tolylsulfonylmethyl isocyanide or tosylmethyl isocyanide. It is the best‐known member of a series of about 25 sulfonyl‐substituted methyl isocyanides RSO2CH2NC collected in Chart 1 (p. 426). TosMIC is a multipurpose synthetic reagent. It is by far the most versatile synthon derived from methyl isocyanide. This chapter provides a complete account of the synthetic uses of TosMIC based on a literature search closed in January 1996, and supplemented with further data available to the authors. Also included are applications of some of the more important TosMIC homologs (TosCHRNC).TosMIC is the only commercially available sulfonylmethyl isocyanide. It is a stable, colorless, practically odorless solid, which can be stored at room temperature without decomposition.Four brief review papers on the chemistry of TosMIC have appeared, in 1980, 1987, 1993, and 1995. Several reviews on the chemistry of isocyanides in general are available.An effort has been made to make this chapter as complete as possible, in coverage both by tables and by references, with respect to the immediate objective: a survey of the “Synthetic Uses of TosMIC.” Emphasis is on the primary products derived from reactions of TosMIC and related isocyanides, with limited reference to the further utilization of these products. Thus, the next section gives a complete account of reductive cyanation, the conversion of aldehydes or ketones into cyanides with the use of TosMIC, but for obvious reasons synthetic applications of the product cyanides are not treated in this chapter. One of the subsequent sections describes the application of TosMIC to the synthesis of pyrroles, including 2,3‐divinylpyrroles, which are important precursors in a new synthesis of indoles. This latter transformation, made possible by the easy availability of the precursors through TosMIC chemistry, is afforded brief coverage.As a rule, reference to preliminary papers has been omitted when the same information is available from the corresponding full papers. The patent literature is covered highly selectively and is cited only when providing new and relevant information. Negative results of reactions are reported in the text or tables only when at least some relevant information is available with respect to the conditions of such unsuccessful attempts.
α‐Hydroxylation of Enolates and Silyl Enol Ethers
Authors: Chen Bang‐Chi , Zhou Ping , Davis Franklin A. , Ciganek Engelbert 
Published: April 2004

AbstractThe autoxidation of enolizable carbonyl compounds was reported as early as 1871, and the accelerating action of base is well documented. The products of these reactions, however, were usually mixtures of compounds resulting from decomposition of the unstable alpha‐hydroperoxy intermediates. It was not recognized until the 1960s that these intermediates can be reduced to alpha‐hydroxy compounds with zinc dust. This observation laid the foundation for what has become on of the simplest and most widely used strategies for introducing a hydroxyl group adjacent to a carbonyl group, namely the oxidation of metal enolates. The alpha‐hydroxy carbonyl array not only occurs in many biologically active molecules, but also serves as an important building block for synthesis.While the oxygenation of enolates still play an important role in the synthesis of alpha‐hydroxy carbonyl compounds, a variety of new, more convenient oxididizing agents, including chiral nonracemic ones, have been introduced. In addition, sily enol ethers and silyl ketene acetals can serve as educts for alpha‐hydroxycarbonyl compounds. This chapter covers the literature of alpha‐hydroxylation of metal enolates and silyl enol ethers up to the end of 2000. Nitriles and aza‐enolates are included. The related alpha‐alkoxylation, alpha‐acyloxylation, and alpha‐sulfonyloxylation of metal enolates are briefly discussed.
Hydroformylation of high‐molecular‐weight cis‐1,4‐polybutadiene catalyzed by HRH(CO)(PPh3)3
Authors: Im‐Erbsin Sasisom , Prasassarakich Pattarapan , Rempel Garry L. 
Published: April 2004

AbstractThe kinetics of the hydroformylation of high‐molecular‐weight cis‐1,4‐polybutadiene in the presence of HRh(CO)(PPh3)3 and monochlorobenzene as a solvent were studied. The degree of conversion was examined by spectroscopic characterization with Fourier transform infrared and 1H‐NMR analysis. According to the 24‐factorial experimental design, the temperature, catalyst concentration, and pressure appear to be significant factors for the hydroformylation of cis‐1,4‐polybutadiene. The kinetic studies indicated that the hydroformylation was first‐order with respect to the catalyst and carbon–carbon double‐bond concentrations and H2/CO pressure (1:1 ratio). The effects of the H2/CO ratio in the synthesis gas and added triphenyl phosphine were also studied. The apparent activation energy for the hydroformylation of cis‐1,4‐polybutadiene over the temperature range of 60–80°C was estimated to be 41 kJ/mol. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 854–869, 2004
Self‐reinforcing elastomer composites based on ethylene–propylene–diene monomer rubber and liquid‐crystalline polymer
Authors: Chakraborty S. , Sahoo N. G. , Jana G. K. , Das C. K. 
Published: April 2004

AbstractIn this study, the prime factor determining the size, shape, and distribution of liquid‐crystalline polymer (LCP) was the viscosity ratio at the processing conditions. The fiber‐forming capacity of the LCP depended on the viscosity of the ethylene–propylene–diene monomer rubber (EPDM). With increasing LCP content, the tensile and tear strengths did not increase, perhaps because of incompatibility between the EPDM and LCP. The hardness increased because of the hard mesogenic groups in the LCP. The percentage swelling decreased as the LCP content increased. With increasing LCP content, processability became easier because of a lower melt viscosity. The scorch time increased at higher LCP levels. A higher percentage crystallinity was observed with increasing LCP content. Scanning electron microscopy clearly showed the fiber phase formation, which was two‐dimensionally isotropic in nature, confirming fiber formation even in a shear field. The addition of LCP improved the thermal stability. The onset degradation temperatures shifted to higher values with increasing LCP content. Dynamic mechanical thermal analysis revealed that with the addition of LCP, the mechanical damping increased at its lower level. High‐temperature processing increased the effective amorphous zone. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 711–718, 2004
Polyimides 6: Synthesis, characterization, and comparison of properties of novel fluorinated poly(ether imides)
Authors: Banerjee Susanta , Madhra Mukesh Kumar , Kute Vijay 
Published: April 2004

AbstractFive new poly(ether imides) have been prepared on reaction with oxydiphthalic anhydride (ODA) with five different diamines: 1,4‐bis(p‐aminophenoxy‐2′‐trifluoromethyl benzyl) benzene, 4,4′‐bis(p‐aminophenoxy‐2′‐trifluoromethyl benzyl) benzene, 1,3‐bis(p‐aminophenoxy‐2′‐trifluoromethyl benzyl) benzene, 2,6‐bis(p‐aminophenoxy‐2′‐trifluoromethyl benzyl) pyridine, and 2,5‐bis(p‐aminophenoxy‐2′‐trifluoromethyl benzyl) thiophene. Synthesized polymers showed good solubility in different organic solvents. The polyimide films have low water absorption of 0.3–0.7%, low dielectric constants of 2.82–3.19 at 1 MHz, and high optical transparency at 500 nm (>73%). These polyimides showed very high thermal stability with decomposition temperatures (5% weight loss) up to 531°C in air and good isothermal stability; only 0.4% weight loss occurred at 315°C after 5 h. Transparent thin films of these polyimides exhibited tensile strength up to 147 MPa, a modulus of elasticity up to 2.51 GPa and elongation at break up to 30% depending upon the repeating unit structure. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 821–832, 2004
Complex interactions among additive/supercritical CO2/polymer ternary systems and factors governing the impregnation efficiency
Authors: Xu Qun , Chang Yuning 
Published: April 2004

AbstractStyrene and acrylic acid were impregnated into a series of polyamide products (nylon1212, nylon1010, nylon66, nylon6) using supercritical CO2 as the additive‐carrier and substrate‐swelling agent. The impregnation efficiency of low molecular weight additives into substrates is attributed to complicated interactions among the system: (1) loading of additives in substrates, (2) dissolving of additives in CO2 phase, (3) swelling and plasticizing of substrates by CO2. For the first time solubility parameter was introduced to discuss the impregnation efficiency. It was found that the relative solubility of additive in the polymer substrate and CO2 is a major factor governing the incorporated amount; yet swelling of the substrate and CO2‐induced crystallization also contribute to the value. The study generalizes complex factors influencing the impregnation possibility of different systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 742–748, 2004
From two‐step flow to the Internet: The changing array of sources for genetics information seeking
Authors: Case Donald O. , Johnson J. David , Andrews James E. , Allard Suzanne L. , Kelly Kimberly M. 
Published: April 2004

AbstractThe diffusion of the Internet has radically expanded the readily available sources for information of all types. Information that was once obtained second‐hand from friends and acquaintances—the traditional “two‐step flow”—is now found easily through the Internet. The authors make use of survey data to explore this thesis in regards to information sources about genetic testing and the influence of the Internet on the information seeking behaviors of the public. A telephone survey of a random sample of 882 adults asked them about their knowledge of, concerns about, and interest in genetic testing. Respondents were most likely to first turn to the Internet for information about cancer genetics, second to public libraries, and third to medical doctors. Overall, doctors were the most likely source to be consulted when second and third choices are considered. Age, income, and self‐reported understanding of genetics are shown to be predictors of whether someone goes to medical professionals for advice, rather than to the Internet or public library. The results raise questions about the apparent tendency of the public to regard the Internet as the best source of information on complex topics like genetics, for which it may be ill‐suited.
Engineering green fluorescent protein as a dual functional tag
Authors: Paramban Rosanto I. , Bugos Robert C. , Wen Su Wei 
Published: April 2004

AbstractA hexa‐histidine (6 × His) sequence was inserted into a surface loop of the green fluorescent protein (GFP) to develop a dual functional GFP useful for both monitoring and purification of recombinant proteins. Two variants (GFP172 and GFP157), differentiated by the site of insertion of the 6×His sequence, were developed and compared with a control variant (GFPHis) having the 6×His sequence at its C‐terminus. The variants were produced in Escherichia coli and purified using immobilized metal affinity chromatography (IMAC). The purification efficiencies by IMAC for all variants were found to be comparable. Purified GFP172 and GFP157 variants retained ∼60% of the fluorescence compared to that of GFPHis. The reduction in the fluorescence intensity associated with GFP172 and GFP157 was attributed to the lower percentage of fluorescent GFP molecules in these variants. Nonetheless, the rates of fluorescence acquisition were found to be similar for all functional variants. Protein misfolding at an elevated temperature (37°C) was found to be less profound for GFP172 than for GFP157. The dual functional properties of GFP172 were tested with maltose binding protein (MBP) as the fusion partner. The MBP‐GFP172 fusion protein remained fluorescent and was purified from E. coli lysate as well as from spiked tobacco leaf extracts in a single‐step IMAC. For the latter, a recovery yield of ∼75% was achieved and MBP‐GFP172 was found to coelute with a degraded product of the fusion protein at a ratio of about 4:1. The primary advantage of the chimeric GFP tag having an internal hexa‐histidine sequence is that such a tag allows maximum flexibility for protein or peptide fusions since both N‐ and C‐terminal ends of the GFP are available for fusion. © 2004 Wiley Periodicals, Inc.
Metal‐Complex Assemblies Constructed from the Flexible Hinge‐Like Ligand H2bhnq: Structural Versatility and Dynamic Behavior in the Solid State
Authors: Yamada Koichi , Yagishita Sadahiro , Tanaka Hirokazu , Tohyama Kazuhiro , Adachi Keiichi , Kaizaki Sumio , Kumagai Hitoshi , Inoue Katsuya , Kitaura Ryo , Chang Ho‐Chol , Kitagawa Susumu , Kawata Satoshi 
Published: April 2004

AbstractNovel metal‐complex assemblies constructed from the flexible hinge‐like ligand H2bhnq (H2bhnq=2,2′‐bi(3‐hydroxy‐1,4‐naphthoquinone)) have been synthesized. The X‐ray crystal structures of these compounds reveal that four types of architectures are accessible by variation of the metal ions. In copper(II) compounds 1–3, the chelating bhnq2− ions bridge copper(II) centers to form one‐dimensional zigzag chains. The chains of 1–3 are arranged by hydrogen‐bonding interactions and stacking interactions to produce porous structures. Cobalt(II) and zinc(II) compounds 4 and 5 form one‐dimensional helical chains. In 4 and 5, the crystal packing induces spontaneous resolution of the helical chains with chiral cavities formed perpendicular to the helices. Nickel(II) compounds 6 and 7 form cyclic tetramers. The fourth architecture, a dimer (compound 8), is obtained by the reaction of zinc(II) and bhnq2− in MeOH. In these compounds, changes of the dihedral angles and the metal‐coordination mode of the bhnq2− ion induce the structural versatility. The assemblies of the zigzag chains of the copper(II) compounds exhibit reversible vapochromic behavior. UV/Vis, powder X‐ray diffraction, EPR, and adsorption isotherm measurements indicate that this vapochromic behavior is based on the hinge‐like flexibility of the bhnq2− ion.
Hormone replacement therapy in relation to breast carcinoma incidence rate ratios
Authors: Tjønneland Anne , Christensen Jane , Thomsen Birthe L. , Olsen Anja , Overvad Kim , Ewertz Marianne , Mellemkjær Lene 
Published: April 2004

AbstractBACKGROUNDThe goal of the current study was to investigate the relation between hormone replacement therapy (HRT) and breast carcinoma in a prospective study cohort. Particular attention was paid to the type of HRT used and to the association of HRT type with estrogen receptor status and tumor histology.METHODSBetween 1993 and 1997, a total of 29,875 women were enrolled in the Danish Cancer Society's prospective “Diet, Cancer and Health” study. Among 23,618 women who were assumed to be postmenopausal and for whom information on HRT use was available, we identified 423 cases of breast carcinoma over a median follow‐up period of 4.8 years. Statistical analyses were based on the Cox proportional hazards model, with age serving as the time parameter.RESULTSThe breast carcinoma incidence rate ratio (IRR) was 2.22 (95% confidence interval [CI], 1.80–2.75) for users of HRT at baseline compared with women who never received HRT. Among HRT users (relative to nonusers), the IRR for estrogen receptor–positive tumors (2.38; 95% CI, 1.84–3.06) was greater than the IRR for estrogen receptor–negative tumors (1.56; 95% CI, 1.00–2.43). HRT use at baseline also was analyzed in relation to the incidence of lobular carcinoma and the incidence of ductal carcinoma; the adjusted IRR associated with HRT use was 3.53 (95% CI, 1.94–6.41) for lobular carcinoma and 2.10 (95% CI, 1.64–2.70) for ductal carcinoma. The likelihood of developing estrogen receptor–positive breast carcinoma was found to depend significantly on the type of HRT regimen used (P = 0.03), with women receiving continuous therapy having the greatest probability of developing estrogen receptor–positive disease.CONCLUSIONSAn increased breast carcinoma IRR was found to be associated with current HRT use. In addition, relative to other types of HRT regimens, continuous estrogen + progestin regimens were found to be associated with an increased risk of breast carcinoma, and particularly estrogen receptor–positive breast carcinoma. Cancer 2004. © 2004 American Cancer Society.
Preferential brain locations of low‐grade gliomas
Authors: Duffau Hugues , Capelle Laurent 
Published: April 2004

AbstractBACKGROUNDThe objectives of this study were to register the brain locations in a consecutive series of low‐grade gliomas (LGGs) and compare these localizations with the locations of de novo glioblastomas (GBMs) that were collected during the same period in an effort to analyze whether LGGs are situated in preferential areas and to review the pathophysiologic hypothesis of such a phenomenon.METHODSOne hundred thirty‐two patients with LGG and 102 patients with GBM who were followed consecutively between 1996 and 2003 by the authors were reviewed, whatever their treatment. Using anatomic, three‐dimensional magnetic resonance imaging, the location of each tumor was analyzed accurately according to a classification system based on the proximity of eloquent areas previously reported by the authors.RESULTSOne hundred nine LGGs (82.6%), compared with 55 GBMs (53.9%), were situated within functional regions (P < 0.001). More specifically, 36 LGGs (27.3%), compared with 11 GBMs (10.8%), were localized in the region of the supplementary motor area (SMA) (P < 0.001); and 33 LGGs (25%), compared with 11 GBMs (10.8%), were located within the insula (P < 0.001).CONCLUSIONSThe current findings suggest that LGGs are located preferentially in “secondary” functional areas (immediately near the so‐called primary eloquent regions), especially within the SMA and the insular lobe. This preferential localization may be explained by developmental, cytomyeloarchitectonic, neurochemical, metabolic, and functional reasons. A better knowledge of the pathophysiologic mechanisms underlying preferential LGGs locations may improve understanding of the genesis and natural history of these tumors and, subsequently, their management. Cancer 2004. © 2004 American Cancer Society.
Numerical methods for one‐dimensional Stefan problems
Authors: Caldwell J. , Kwan Y. Y. 
Published: April 2004

AbstractThis paper describes and compares several effective methods for the numerical solution of one‐dimensional Stefan problems. It is not intended to be an exhaustive review but is restricted to a range of problems and geometries including melting in the half‐plane, outward cylindrical solidification and outward spherical solidification. From the limited comparison of numerical results obtained, some helpful comments can be made which may prove valuable in the future use of these methods. Copyright © 2004 John Wiley & Sons, Ltd.