Home About us Contact
|
Home About us Contact | ||
|
|
||
Auxiliary
Kinds of Auxiliary Terms modified by Auxiliary Selected Abstracts2,5-Disubstituted Pyrrolidines as Chiral Auxiliaries in Radical Reactions: A Theoretical ApproachEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2010Miglena K. Georgieva Abstract The radical addition to amides derived from chiral 2,5-disubstituted pyrrolidines has been theoretically studied by the use of density functional methods and the results compared with known experimental data. The results agree quite well with those obtained experimentally and allow the full rationalization of the factors influencing the diastereoselectivity. Steric effects are the main factors determining the selectivity, but electronic interactions can also be very important when the attacking alkene is ,,,-conjugated, as in acrylic esters or acrylamides. Additions at the ,- and ,-positions of the amide chain in the auxiliary are subject to different rules, with the former usually yielding high diastereoselectivities both experimentally and theoretically, whereas the latter is theoretically predicted to occur with low selectivity. We fully rationalize these two opposite behaviours and suggest several ways to circumvent this limitation, thus strongly increasing the interest of this type of structure as chiral auxiliaries in radical reactions. [source] Diastereoselective Reactions of the Tiglic Acid Functionality Mediated by Oxazolidine Chiral Auxiliaries: A Mechanistic Comparison of DMD andm -CPBA Epoxidations versus Singlet Oxygen and PTAD Ene ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2005Aurelia Pastor Abstract 2,2-Dimethyloxazolidines have been utilized as chiral auxiliaries for the diastereoselective functionalization of the optically active tiglic acid derivatives (S)- 1 by means of epoxidation with DMD or m -CPBA and ene reactions with 1O2 or PTAD. In the DMD and m -CPBA epoxidations, high diastereoselectivities but opposite senses of diastereomer selection were observed. In contrast, the stereochemistry of the 1O2 and PTAD ene reactions depended on the size of the attacking enophile: whereas essentially perfect diastereoselectivity was obtained with PTAD, much lower stereoselection was observed with 1O2. The stereochemical results for the DMD and m -CPBA epoxidations and the PTAD ene reaction are explained in terms of the energy differences for the corresponding diastereomeric transition states, dictated by steric and electronic effects. The PTAD ene reaction for these tiglic acids (S)- 1 provides, after removal of the chiral auxiliaries, an attractive synthetic route for optically active ,-amino acid derivatives.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Synthesis of Reactive Polymeric Dyes as Textile AuxiliariesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 9 2003Angelina Altomare Abstract New polymeric materials containing amino-substituted azobenzene chromophores and reactive functional groups and characterized by some hydrophilicity were prepared with the aim of investigating alternative textile dyeing routes. The indicated materials were obtained either by copolymerization of suitable monomers or by modification of preformed polymers. In both cases commercial 4-amino-2,,3-dimethylazobenzene (FG) was used as chromogenic compound. According to the first synthetic strategy, the methacrylamido derivative of FG was copolymerized by free radical initiation with different monomers, such as methyl methacrylate, glycidyl methacrylate, N - tert -butylacrylamide, methacrylic acid, N -vinyl-2-pyrrolidinone, and vinyl acetate. Reaction of FG with preformed polymers containing epoxy groups generally afforded crosslinked materials. On the other hand, low FG loading extents were recorded by amidation of polymers containing carboxylic groups. Indeed, almost quantitative conversions were obtained only in the reaction of FG with anhydride containing polymers. The chemical structure, molecular weight properties, and the physical-chemical characteristics of all synthesized polymeric dyes were thoroughly investigated. Some very preliminary dyeing tests of different cloth types with the prepared polymeric dyes were also performed. UV absorption spectrum of poly(FGMAA) and poly(FGMAA- co -MMA) in chloroform at 25,°C (FGMAA,=,4-methacrylamido-2,,3-dimethylazobenzene). [source] ChemInform Abstract: Regiodivergent Approach to ,- and ,-(Arylthio)alkenylphosphane Oxides and Sulfides: Aminophosphanes as Synthetic Auxiliaries.CHEMINFORM, Issue 18 2009Mateo Alajarin Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Asymmetric Epoxidation, Michael Addition, and Triple Cascade Reaction Using Polymer-Supported Prolinol-Based Auxiliaries.CHEMINFORM, Issue 8 2009Michael C. Varela Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Diastereoselective Epoxidation of N-Enoylsultams with Different Chiral Sultams as Auxiliaries.CHEMINFORM, Issue 37 2006Shu-Jia Zhang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] 3,5-Dialkyl Effect on Enantioselectivity in Pd Chemistry: Applications Involving Both Bidentate and Monodentate Auxiliaries.CHEMINFORM, Issue 36 2004Pascal Dotta No abstract is available for this article. [source] New S,O-Acetals from (1R)-(-)-Myrtenal as Chiral Auxiliaries in Nucleophilic Additions.CHEMINFORM, Issue 24 2004Luis Chacon-Garcia Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis of Optically Pure Arylsilylcarbinols and Their Use as Chiral Auxiliaries in Oxacarbenium Ion Reactions.CHEMINFORM, Issue 21 2004John R. Huckins Abstract For Abstract see ChemInform Abstract in Full Text. [source] A General Method for the Asymmetric Synthesis of Both Enantiomers of 1-Substituted 1,2,3,4-Tetrahydro-,-carbolines Employing Pyroglutamic Acid Derivatives as Chiral Auxiliaries.CHEMINFORM, Issue 37 2003Takashi Itoh Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: O-Silylated Steroidal cis-Amino Alcohols as Chiral Auxiliaries: Highly Diastereoselective Pd-Catalyzed Cyclopropanation of ,,,-Unsaturated Aldimines.CHEMINFORM, Issue 29 2002M. Dubs Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: The Influence of Chiral Auxiliaries is Enhanced Within ZeolitesCHEMINFORM, Issue 3 2001Sivaguru Jayaraman Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: New Chiral Auxiliaries for Highly Stereoselective Asymmetric Methoxyselenenylations.CHEMINFORM, Issue 1 2001Thomas G. Back Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Improved Auxiliary for the Synthesis of Medium-Sized Bis(lactams)EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 2 2008Jasper Springer Abstract Our auxiliary-based method for the synthesis of bis(lactams) has been optimized. A novel auxiliary is described that is inserted in the backbone of a linear peptide facilitating the mutually reactive terminal groups to approach one another for a cyclization reaction. A subsequent ring contraction mechanism leads to the bis(lactams) with the remainings of the auxiliary still attached. Functionalized seven- and eight-membered bis(lactams) have been prepared that are difficult to access using traditional methods. Removal of the auxiliary from the bis(lactams) has been described with the possible side reactions that can occur.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Diastereoselective Alkylation of (Arene)tricarbonylchromium and Ferrocene Complexes Using a Chiral, C2 -Symmetrical 1,2-Diamine as AuxiliaryEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2006Alexandre Alexakis No abstract is available for this article. [source] Diastereoselective Alkylation of (Arene)tricarbonylchromium and Ferrocene Complexes Using a Chiral, C2 -Symmetrical 1,2-Diamine as AuxiliaryEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2005Alexandre Alexakis Abstract The aminal of (benzaldehyde)tricarbonylchromium and en-antiopure bipyrrolidine undergoes diastereoselective ortho -metallation with butyllithium. Quenching with various electrophiles, followed by hydrolysis of the aminal, affords ortho -substituted (benzaldehyde)tricarbonylchromium compounds with high ee (91,99,%). When quenched with Ph2PCl, a new chiral P,N-bidentate ligand is obtained, which shows efficiency in Pd- and Cu-catalysed reactions. The aminal of ferrocenecarbaldehyde could also be formed, but the ortho -deprotonation occurs with only moderate diastereoselectivity (70,%). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Crosswell seismic waveguide phenomenology of reservoir sands & shales at offsets >600 m, Liaohe Oil Field, NE ChinaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2005P. C. Leary SUMMARY Crosswell seismic data recorded at 620,650 m offsets in an oil-bearing sand/shale reservoir formation at the Liaohe Oil Field, northeast China, provide robust evidence for waveguide action by low-velocity reservoir layers. Crosswell-section velocity models derived from survey-well sonic logs and further constrained by observed waveguide seismic wavegroup amplitudes and phases yield plausible evidence for interwell reservoir,sand continuity and discontinuity. A pair of back-to-back Liaohe crosswell vector-seismic surveys were conducted using a source well between two sensor wells at 650 and 620 m offsets along a 200-m-thick reservoir formation dipping 7° down-to-east between depths of 2.5 and 3 km. A downhole orbital vibrator generated seismic correlation wavelets with frequency range 50,350 Hz and signal/noise ratio up to 5:1 over local downhole ambient noise. The sensor wells were instrumented with a mobile 12- to 16-level string of clamped vector-motion sensor modules at 5 m intervals. Using 5 m source depth increments, crosswell Surveys 1 and 2 cover source/sensor well intervals above and through the reservoir of, respectively, 600 m/600 m (13 000 vector traces in 9 common sensor fans) and 300 m/560 m (7000 vector traces in 7 common sensor fans). Survey 1 common sensor gathers show clear, consistent high-amplitude 20 ms waveletgroup lags behind the first-arrival traveltime envelope. Such arrivals are diagnostic of seismic low-velocity waveguides connecting the source and sensor wells. Observed Survey 1 retarded wavegroup depths tally with source and sensor depths in low-velocity layers identified in sonic well logs. Finite-difference acoustic model wavefields computed for waveguide acoustic layers constrained by well-log sonic velocity data match the observed waveguide traveltime and amplitude systematics. Model waveforms duplicate the observed m-scale and ms-scale sensitivity of waveguide spatio-temporal energy localization. Survey 2 crosswell data, in contrast, provide no comparable evidence for waveguide action despite a sensor-well sonic well log similar to that of Survey 1. Instead, acoustic wavefield modelling of Survey 2 data clearly favours an interpreted waveguide model with 10° downdip interrupted by a 75,100 m throw down-fault near the sensor well. The absence of clear waveguide arrivals is adequately explained by dispersal of waveguide energy at the fault discontinuity. Auxiliary well sonic velocity and lithologic logs confirm the model-implied 75,100 m of down-throw faulting near the sensor well. [source] Preparation of ,2 -Amino Acid Derivatives (,2hThr, ,2hTrp, ,2hMet, ,2hPro, ,2hLys, Pyrrolidine-3-carboxylic Acid) by Using DIOZ as Chiral Auxiliary,HELVETICA CHIMICA ACTA, Issue 8 2005Francois Gessier The title compounds were prepared from valine-derived N -acylated oxazolidin-2-ones, 1,3, 7, 9, by highly diastereoselective (,,90%) Mannich reaction (,,4,6; Scheme,1) or aldol addition (,,8 and 10; Scheme,2) of the corresponding Ti- or B-enolates as the key step. The superiority of the ,5,5-diphenyl-4-isopropyl-1,3-oxazolidin-2-one' (DIOZ) was demonstrated, once more, in these reactions and in subsequent transformations leading to various t -Bu-, Boc-, Fmoc-, and Cbz-protected ,2 -homoamino acid derivatives 11,23 (Schemes,3,6). The use of , -bromo-acyl-oxazolidinones 1,3 as starting materials turned out to open access to a variety of enantiomerically pure trifunctional and cyclic carboxylic-acid derivatives. [source] Enders' SAMP-Hydrazone as Traceless Auxiliary in the Asymmetric 1,4-Addition of Cuprates to EnonesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Karsten Sammet Abstract Conjugate additions of Gilman cyanocuprates to (S)- N -amino-2-(methoxymethyl)pyrrolidine (SAMP)-hydrazones 4, 5 derived from cyclic and acyclic ,,,-unsaturated ketones were investigated. A protocol utilizing copper(II) sulfate/ammonium chloride was evolved, which allowed cleavage of SAMP (S)- 1 under the hydrolysis and work-up conditions, followed by recovery of the auxiliary with ethylenediaminetetraacetic acid (EDTA). The enantioselectivity of cuprate additions was dominated for cyclic SAMP-hydrazones 4 by the cuprate alkyl substituent and the ring size, in the case of acyclic arylidene SAMP-hydrazones 5, however, by the nature of the aryl substituent. Electron-donating substituents gave poor enantiomeric excesses, whereas electron-withdrawing groups provided excellent ee values of 98,99%. The configuration of the new stereocenter was determined to be (R). Moreover, a reaction sequence was developed which integrates a tandem 1,4-addition/methylation and traceless hydrolytic cleavage of the auxiliary (S)- 1 in a one-pot reaction, resulting in enantiomerically pure methyl ketones 11,13, each of them with>99% ee. [source] Paraconsistent Artificial Neural Network as Auxiliary in Cephalometric DiagnosisARTIFICIAL ORGANS, Issue 7 2010Mauricio C. Mario Abstract This work presents an application of the paraconsistent artificial neural network (PANN) in the analysis of cephalometric variables and provides an orthodontic diagnosis. An expert's analysis is subject to the inherent imprecision of measurements, registers, and individual variability of physician visual analysis. Patient input cephalometric values are compared with means drawn from individuals considered normal in the cephalometric point of view by the PANN. This reference is constituted by individuals from 6 to 18 years old, both genders. The applied cephalometric analysis was targeted to measure skeletal and dental discrepancies and established a cephalometric diagnosis. The analysis results in degrees of skeletal, anteroposterior, and dental discrepancy, pertinent to upper and lower incisors. A sample of 120 orthodontic patients was processed by the proposed model and three orthodontic experts. Comparisons between the model and the human expert's performance provided kappa indexes that varied from moderate to almost perfect agreement. The agreement between the model and specialist's performance was equivalent. In addition, the model pointed out contradictions presented in the data that were not noticed by the orthodontists, which highlight the contribution that this kind of system could carry out in the orthodontics decision support. [source] Ratio Estimation with Measurement Error in the Auxiliary VariateBIOMETRICS, Issue 2 2009Timothy G. Gregoire Summary With auxiliary information that is well correlated with the primary variable of interest, ratio estimation of the finite population total may be much more efficient than alternative estimators that do not make use of the auxiliary variate. The well-known properties of ratio estimators are perturbed when the auxiliary variate is measured with error. In this contribution we examine the effect of measurement error in the auxiliary variate on the design-based statistical properties of three common ratio estimators. We examine the case of systematic measurement error as well as measurement error that varies according to a fixed distribution. Aside from presenting expressions for the bias and variance of these estimators when they are contaminated with measurement error we provide numerical results based on a specific population. Under systematic measurement error, the biasing effect is asymmetric around zero, and precision may be improved or degraded depending on the magnitude of the error. Under variable measurement error, bias of the conventional ratio-of-means estimator increased slightly with increasing error dispersion, but far less than the increased bias of the conventional mean-of-ratios estimator. In similar fashion, the variance of the mean-of-ratios estimator incurs a greater loss of precision with increasing error dispersion compared with the other estimators we examine. Overall, the ratio-of-means estimator appears to be remarkably resistant to the effects of measurement error in the auxiliary variate. [source] ChemInform Abstract: Axial Chirality Control During Suzuki,Miyaura Cross-Coupling Reactions: The tert-Butylsulfinyl Group as an Efficient Chiral Auxiliary.CHEMINFORM, Issue 13 2010Francoise Colobert Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Rhodium-Catalyzed Reformatsky-Type Reaction for Asymmetric Synthesis of Difluoro-,-lactams Using Menthyl Group as a Chiral Auxiliary.CHEMINFORM, Issue 36 2008Atsushi Tarui Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Improved Auxiliary for the Synthesis of Medium-Sized Bis(lactams).CHEMINFORM, Issue 21 2008Jasper Springer Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] 1-(2,4,6-Triisopropylphenyl)ethylamine: A New Chiral Auxiliary for the Asymmetric Synthesis of ,-Amino Acid Derivatives.CHEMINFORM, Issue 21 2007Pascale Cividino Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Nitrile Oxide Cycloaddition Chemistry Using Benzotriazole as a Steric Auxiliary.CHEMINFORM, Issue 22 2006G. Paul Savage Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Application of Axially Dissymmetric Ligand Recoverable with Fluorous Solvent as a Chiral Auxiliary.CHEMINFORM, Issue 20 2006Masaaki Omote Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Enantioselective Phenyl Transfer to Aldehydes Using 1,1,-Bi-2-Naphthol-3,3,-dicarboxamide as Chiral Auxiliary.CHEMINFORM, Issue 51 2005Katsuji Ito Abstract For Abstract see ChemInform Abstract in Full Text. [source] A New Entry to Asymmetric Synthesis of Optically Active ,,,-Substituted ,-Butyrolactones, Using a Carbohydrate Derived Amide as Both a Chiral Auxiliary and a Proton Source.CHEMINFORM, Issue 24 2005Ling-Lin Huang No abstract is available for this article. [source] Diastereoselective Addition Reactions of Furyl Sulfonylimine Using Chiral Boronates as Auxiliary: Application to the Enantioselective Synthesis of 2,3-Disubstituted Furyl Sulfonylamides.CHEMINFORM, Issue 33 2004Ho-Kee Yim Abstract For Abstract see ChemInform Abstract in Full Text. [source] | ||||||||||||||||||||||||||||||||||||||||||||||