The Experts below are selected from a list of 50436 Experts worldwide ranked by ideXlab platform
Alexandre Alexakis - One of the best experts on this subject based on the ideXlab platform.
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construction of enantioenriched Cyclic Compounds by asymmetric allylic alkylation and ring closing metathesis
European Journal of Organic Chemistry, 2013Co-Authors: Francesca Giacomina, Alexandre AlexakisAbstract:A new approach to highly enantioenriched Cyclic Compounds (up to 98 % ee) has been developed by using ω-ethylenic allylic substrates in a one-pot asymmetric allylic alkylation and ring-closing metathesis sequence. The starting Compounds are synthetic equivalents of Cyclic allylic substrates. The method is exemplified with both Cu and Ir catalysts, and chiral phosphoramidite ligands.
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Construction of Enantioenriched Cyclic Compounds by Asymmetric Allylic Alkylation and Ring‐Closing Metathesis
European Journal of Organic Chemistry, 2013Co-Authors: Francesca Giacomina, Alexandre AlexakisAbstract:A new approach to highly enantioenriched Cyclic Compounds (up to 98 % ee) has been developed by using ω-ethylenic allylic substrates in a one-pot asymmetric allylic alkylation and ring-closing metathesis sequence. The starting Compounds are synthetic equivalents of Cyclic allylic substrates. The method is exemplified with both Cu and Ir catalysts, and chiral phosphoramidite ligands.
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Copper-catalyzed enantioselective intramolecular conjugate addition/trapping reactions: synthesis of Cyclic Compounds with multichiral centers.
Chemistry (Weinheim an der Bergstrasse Germany), 2007Co-Authors: Alexandre AlexakisAbstract:The Cu-catalyzed enantioselective conjugate addition of dialkylzinc to bis-alpha,beta-unsaturated carbonyl Compounds followed by the intramolecular trapping of the zinc enolate in the presence of chiral phosphoramidite ligands was investigated. Cyclic and heteroCyclic Compounds with multichiral centers were formed as a mixture of two diastereomers with excellent diastereoselectivities (up to 99:1) and enantioselectivities (up to 94 % ee, ee=enantiomeric excess). The stereochemistry was determined to be trans,trans for the major products and trans,cis for the minor products. The absolute configuration of the Cyclic Compounds was assigned by comparison with the analogous adduct derived from trans-3-nonen-2-one and Et(2)Zn or the adduct obtained through conjugate addition of Me(2)Zn to trans-1-phenyl-non-2-en-1-one. Further transformation of these Cyclic products into more complex Compounds is under investigation in our laboratory.
Francesca Giacomina - One of the best experts on this subject based on the ideXlab platform.
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construction of enantioenriched Cyclic Compounds by asymmetric allylic alkylation and ring closing metathesis
European Journal of Organic Chemistry, 2013Co-Authors: Francesca Giacomina, Alexandre AlexakisAbstract:A new approach to highly enantioenriched Cyclic Compounds (up to 98 % ee) has been developed by using ω-ethylenic allylic substrates in a one-pot asymmetric allylic alkylation and ring-closing metathesis sequence. The starting Compounds are synthetic equivalents of Cyclic allylic substrates. The method is exemplified with both Cu and Ir catalysts, and chiral phosphoramidite ligands.
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Construction of Enantioenriched Cyclic Compounds by Asymmetric Allylic Alkylation and Ring‐Closing Metathesis
European Journal of Organic Chemistry, 2013Co-Authors: Francesca Giacomina, Alexandre AlexakisAbstract:A new approach to highly enantioenriched Cyclic Compounds (up to 98 % ee) has been developed by using ω-ethylenic allylic substrates in a one-pot asymmetric allylic alkylation and ring-closing metathesis sequence. The starting Compounds are synthetic equivalents of Cyclic allylic substrates. The method is exemplified with both Cu and Ir catalysts, and chiral phosphoramidite ligands.
M. Ali Haider - One of the best experts on this subject based on the ideXlab platform.
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Mechanistic Approaches toward Rational Design of a Heterogeneous Catalyst for Ring-Opening and Deoxygenation of Biomass-Derived Cyclic Compounds
ACS Sustainable Chemistry & Engineering, 2019Co-Authors: Shelaka Gupta, Imteyaz Alam, Tuhin Suvra Khan, M. Ali HaiderAbstract:Technologies for the processing of lignocellulosic biomass into fuels and chemicals are generally focused on selective chemical transformation of the three different types of constituents: cellulose, hemicellulose and lignin. In this regard, heterogeneous catalytic reactions are employed to defunctionalize and upgrade the platform molecules obtained selectively from these constituents. Herein, a selection of studies are discussed which are adapted to deoxygenate and valorize the biomass-derived platform molecules with a specific focus on understanding the reaction mechanisms and rational design of a heterogeneous catalyst. The selection of the deoxygenation process constituted a combination of two or three reactions. For example, ring-opening reactions of the Cyclic Compounds are studied with decarboxylation, dehydration, hydrogenation and/or Diels–Alder reaction carried out on metal, acid and/or oxide catalysts. The platform molecules studied here include an array of saturated lactones, 2-pyrones, Cyclic...
Kensuke Naka - One of the best experts on this subject based on the ideXlab platform.
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Polymers and Cyclic Compounds based on a side‐opening type cage silsesquioxane
Journal of Polymer Science Part A: Polymer Chemistry, 2019Co-Authors: Hiroaki Imoto, Yuri Sato, Kensuke NakaAbstract:Polymers having polyhedral oligomeric silsesquioxane (POSS) in the main chains are an important class of organic–inorganic hybrid materials. Despite the increasing attention to the POSS polymers, variation of the monomers is still limited. Herein, we have proposed side‐opening POSS (SO‐POSS) monomers. Platinum‐catalyzed hydrosilylation polymerization proceeded to produce polysiloxanes having SO‐POSS in the main chains. The obtained polysiloxanes showed good solubility, high thermal stability, high transparency, and tunable reflective index. In addition, Cyclic Compounds were obtained during the investigation of the polymerization, and were synthesized with high selectivity under the slightly diluted conditions. The obtained Cyclic Compounds showed high thermal stability due to the silsesquioxane backbone, and the high dispersibility as a filler in poly(methyl methacrylate) was demonstrated. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2243–2250
S. Derenne - One of the best experts on this subject based on the ideXlab platform.
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Analytical TMAH pyrolysis of dipeptides: Formation of new complex Cyclic Compounds related to the presence of the peptide bond
Journal of Analytical and Applied Pyrolysis, 2013Co-Authors: J. Templier, N. Gallois, S. DerenneAbstract:To evaluate the influence of the peptide bond on the nature of pyrolysis products released from proteinaceous material, 16 dipeptides were subjected to pyrolysis in the presence of TMAH. The pyrolysis products were identified by GC-MS and compared to those obtained from corresponding single amino acids. Most of the main dipeptide pyrolysis products do not correspond to the major products released upon pyrolysis of the constitutive amino acids. Depending on the considered dipeptide, different mechanisms were shown to be responsible for the formation of the major pyrolysis products. An important pathway, due to TMAH, is the direct methylation of the peptide, along with the formation of piperazine-2,5-diones (DKPs) previously observed from single amino acids. Besides these simple Compounds, the formation of new Cyclic Compounds, more complex cyclisation derivatives based on three amino acids and Cyclic products related to imidazolidinones, was revealed. Based on their structure, different possible mechanisms of formation are proposed for these Cyclic Compounds. It must be noted that no general trend, related to structure or polarity of the amino acids constituent of the dipeptides, allows predicting the nature of their pyrolysis products. However it can be noticed that the formation of imidazolidinone is only observed when the dipeptide contains an OH group in an aliphatic side chain. Comparison between symmetric or almost symmetric dipeptides as Met-Leu/Leu-Met or Val-Thr/Thr-Leu shows that complex DKPs are only formed from one of the dipeptide, highlighting the importance of the C- or N-terminal position of the amino acids. In most cases, the side chain from at least one constitutive amino acid is identifiable in these Cyclic Compounds thus evidencing the contribution of this amino acid. These products can thus be used as markers in addition to the well-known simple DKPs. (C) 2013 Elsevier B.V. All rights reserved.
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Analytical TMAH pyrolysis of dipeptides: Formation of new complex Cyclic Compounds related to the presence of the peptide bond
Journal of Analytical and Applied Pyrolysis, 2013Co-Authors: J. Templier, N. Gallois, S. DerenneAbstract:Abstract To evaluate the influence of the peptide bond on the nature of pyrolysis products released from proteinaceous material, 16 dipeptides were subjected to pyrolysis in the presence of TMAH. The pyrolysis products were identified by GC–MS and compared to those obtained from corresponding single amino acids. Most of the main dipeptide pyrolysis products do not correspond to the major products released upon pyrolysis of the constitutive amino acids. Depending on the considered dipeptide, different mechanisms were shown to be responsible for the formation of the major pyrolysis products. An important pathway, due to TMAH, is the direct methylation of the peptide, along with the formation of piperazine-2,5-diones (DKPs) previously observed from single amino acids. Besides these simple Compounds, the formation of new Cyclic Compounds, more complex cyclisation derivatives based on three amino acids and Cyclic products related to imidazolidinones, was revealed. Based on their structure, different possible mechanisms of formation are proposed for these Cyclic Compounds. It must be noted that no general trend, related to structure or polarity of the amino acids constituent of the dipeptides, allows predicting the nature of their pyrolysis products. However it can be noticed that the formation of imidazolidinone is only observed when the dipeptide contains an OH group in an aliphatic side chain. Comparison between symmetric or almost symmetric dipeptides as Met-Leu/Leu-Met or Val-Thr/Thr-Leu shows that complex DKPs are only formed from one of the dipeptide, highlighting the importance of the C- or N-terminal position of the amino acids. In most cases, the side chain from at least one constitutive amino acid is identifiable in these Cyclic Compounds thus evidencing the contribution of this amino acid. These products can thus be used as markers in addition to the well-known simple DKPs.
