The Experts below are selected from a list of 2589 Experts worldwide ranked by ideXlab platform
Alison J Frontier - One of the best experts on this subject based on the ideXlab platform.
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No Acid Required: 4π and 6π Electrocyclization Reactions of Dienyl Diketones for the Synthesis of Cyclopentenones and 2H‑Pyrans
2016Co-Authors: Steven D Jacob, Joshua L Brooks, Alison J FrontierAbstract:ABSTRACT: The 1,6-conjugate addition of nucleophiles to dienyl diketones produces either Cyclopentenone or 2H-pyran products with high selectivity through either Nazarov (4π) or 6π electrocyclization, respectively. The outcome of the reaction is dependent upon the nature of the nucleophile used. Nucleophiles that are anionic or easily deprotonated exclusively produce Cyclopentenones via Nazarov cyclization, whereas the neutral nucleophile DABCO promotes 6π cyclization to afford 2H-pyrans. Experimental evidence is presented for both retro-4π and-6π electrocyclization in these systems, lending support to the bifurcated mechanistic hypothesis proposed for these cyclizations. Electrocyclic reactions are becoming increasingly valuable in synthesis as chemists continue to develop new methods for catalyzing these cyclizations.1 In recent years, mild catalytic methods for achieving neutral,2 cationic,3 and anionic
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no acid required 4π and 6π electrocyclization reactions of dienyl diketones for the synthesis of Cyclopentenones and 2h pyrans
Journal of Organic Chemistry, 2014Co-Authors: Steven D Jacob, Joshua L Brooks, Alison J FrontierAbstract:The 1,6-conjugate addition of nucleophiles to dienyl diketones produces either Cyclopentenone or 2H-pyran products with high selectivity through either Nazarov (4π) or 6π electrocyclization, respectively. The outcome of the reaction is dependent upon the nature of the nucleophile used. Nucleophiles that are anionic or easily deprotonated exclusively produce Cyclopentenones via Nazarov cyclization, whereas the neutral nucleophile DABCO promotes 6π cyclization to afford 2H-pyrans. Experimental evidence is presented for both retro-4π and -6π electrocyclization in these systems, lending support to the bifurcated mechanistic hypothesis proposed for these cyclizations.
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oxidation initiated nazarov cyclization of vinyl alkoxyallenes
Organic Letters, 2011Co-Authors: William T Spencer, Mark D Levin, Alison J FrontierAbstract:A mild method for the diastereoselective formation of C4, C5-disubstituted Cyclopentenones has been developed, involving formation of a pentadienyl cation via diastereoselective oxidation of a vinyl alkoxyallene. Conrotatory electrocyclization provides the Cyclopentenone product. The broad scope, mild conditions, and uncommon substitution pattern accessible through this transformation make it a useful addition to the existing repertoire of Cyclopentenone synthetic methods.
Jeanhilaire Saurat - One of the best experts on this subject based on the ideXlab platform.
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a toxicologic and dermatologic assessment of cyclopentanones and Cyclopentenones when used as fragrance ingredients
Food and Chemical Toxicology, 2012Co-Authors: D Belsito, David R Bickers, M Bruze, P Calow, M L Dagli, W Dekant, Allison Fryer, Helmut Greim, Yoshiki Miyachi, Jeanhilaire SauratAbstract:The cyclopentanone and Cyclopentenone group of fragrance ingredients was critically evaluated for safety following a complete literature search. For high end users, calculated maximum dermal exposures vary from 0.002% to 15.16% in hydroalcoholic products; systemic exposures vary from 0.0003 to 0.7122 mg/kg/day. The cyclopentanones and Cyclopentenones had a low order of acute toxicity and no significant toxicity in repeat dose studies. No mutagenic or genotoxic activity in bacteria and mammalian cell line assays was observed. Developmental toxicity was not observed. Minimal evidence of skin irritation in humans is associated with current levels of use. Eleven materials were tested undiluted for eye irritation; three were considered irritants. No phototoxic and photosensitization reactions were seen with nine materials tested. At concentrations higher than current reported use, 14 materials were non-sensitizing in HRIPT or maximization tests. 2-Hexylidene cyclopentanone, 2-heptylidenecyclopentan-1-one and 3-methyl-2-(pentyloxy)-2-cyclopenten-1-one are weak sensitizers and have IFRA Standards. Risk of sensitization to the cyclopentanones and Cyclopentenones is generally small under current levels of use. The Panel is of the opinion that there are no safety concerns for the cyclopentanones and Cyclopentenones at reported levels of use and exposure as fragrance ingredients. (C) 2012 Elsevier Ltd. All rights reserved. (Less)
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a toxicologic and dermatologic assessment of cyclopentanones and Cyclopentenones when used as fragrance ingredients
Food and Chemical Toxicology, 2012Co-Authors: D Belsito, David R Bickers, M Bruze, P Calow, M L Dagli, W Dekant, Helmut Greim, Yoshiki Miyachi, A D Fryer, Jeanhilaire SauratAbstract:The cyclopentanone and Cyclopentenone group of fragrance ingredients was critically evaluated for safety following a complete literature search. For high end users, calculated maximum dermal exposures vary from 0.002% to 15.16% in hydroalcoholic products; systemic exposures vary from 0.0003 to 0.7122 mg/kg/day. The cyclopentanones and Cyclopentenones had a low order of acute toxicity and no significant toxicity in repeat dose studies. No mutagenic or genotoxic activity in bacteria and mammalian cell line assays was observed. Developmental toxicity was not observed. Minimal evidence of skin irritation in humans is associated with current levels of use. Eleven materials were tested undiluted for eye irritation; three were considered irritants. No phototoxic and photosensitization reactions were seen with nine materials tested. At concentrations higher than current reported use, 14 materials were non-sensitizing in HRIPT or maximization tests. 2-Hexylidene cyclopentanone, 2-heptylidenecyclopentan-1-one and 3-methyl-2-(pentyloxy)-2-cyclopenten-1-one are weak sensitizers and have IFRA Standards. Risk of sensitization to the cyclopentanones and Cyclopentenones is generally small under current levels of use. The Panel is of the opinion that there are no safety concerns for the cyclopentanones and Cyclopentenones at reported levels of use and exposure as fragrance ingredients.
Susanne Berger - One of the best experts on this subject based on the ideXlab platform.
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tga transcription factors and jasmonate independent coi1 signalling regulate specific plant responses to reactive oxylipins
Journal of Experimental Botany, 2013Co-Authors: Henrik U Stotz, Martin J Mueller, Stefan Mueller, Maria Zoeller, Susanne BergerAbstract:Jasmonates and phytoprostanes are oxylipins that regulate stress responses and diverse physiological and developmental processes. 12-Oxo-phytodienoic acid (OPDA) and phytoprostanes are structurally related electrophilic Cyclopentenones, which activate similar gene expression profiles that are for the most part different from the action of the cyclopentanone jasmonic acid (JA) and its biologically active amino acid conjugates. Whereas JA–isoleucine signals through binding to COI1, the bZIP transcription factors TGA2, TGA5, and TGA6 are involved in regulation of gene expression in response to phytoprostanes. Here root growth inhibition and target gene expression were compared after treatment with JA, OPDA, or phytoprostanes in mutants of the COI1/MYC2 pathway and in different TGA factor mutants. Inhibition of root growth by phytoprostanes was dependent on COI1 but independent of jasmonate biosynthesis. In contrast, phytoprostane-responsive gene expression was strongly dependent on TGA2, TGA5, and TGA6, but not dependent on COI1, MYC2, TGA1, and TGA4. Different mutant and overexpressing lines were used to determine individual contributions of TGA factors to Cyclopentenone-responsive gene expression. Whereas OPDA-induced expression of the cytochrome P450 gene CYP81D11 was primarily regulated by TGA2 and TGA5, the glutathione S-transferase gene GST25 and the OPDA reductase gene OPR1 were regulated by TGA5 and TGA6, but less so by TGA2. These results support the model that phytoprostanes and OPDA regulate differently (i) growth responses, which are COI1 dependent but jasmonate independent; and (ii) lipid stress responses, which are strongly dependent on TGA2, TGA5, and TGA6. Identification of molecular components in Cyclopentenone signalling provides an insight into novel oxylipin signal transduction pathways.
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general detoxification and stress responses are mediated by oxidized lipids through tga transcription factors in arabidopsis
The Plant Cell, 2008Co-Authors: Stefan O Mueller, Beate Hilbert, Katharina Dueckershoff, Thomas Roitsch, Markus Krischke, Martin J Mueller, Susanne BergerAbstract:12-oxo-phytodienoic acid and several phytoprostanes are Cyclopentenone oxylipins that are formed via the enzymatic jasmonate pathway and a nonenzymatic, free radical-catalyzed pathway, respectively. Both types of Cyclopentenone oxylipins induce the expression of genes related to detoxification, stress responses, and secondary metabolism, a profile clearly distinct from that of the cyclopentanone jasmonic acid. Microarray analyses revealed that 60% of the induction by phytoprostanes and 30% of the induction by 12-oxo-phytodienoic acid was dependent on the TGA transcription factors TGA2, TGA5, and TGA6. Moreover, treatment with phytoprostanes and 12-oxo-phytodienoic acid inhibited cell division and root growth, a property also shared by jasmonic acid. Besides being potent signals, Cyclopentenones and other lipid peroxidation products are reactive electrophiles that can covalently bind to and damage proteins. To this end, we show that at least two of the induced detoxification enzymes efficiently metabolize Cyclopentenones in vitro. Accumulation of two of these metabolites was detectable during Pseudomonas infection. The Cyclopentenone oxylipin gene induction profile resembles the defense response induced by a variety of lipophilic xenobiotics. Hence, oxidized lipids may activate chemosensory mechanisms of a general broad-spectrum detoxification network involving TGA transcription factors.
Quanzhong Liu - One of the best experts on this subject based on the ideXlab platform.
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enantioselective formal 4 1 cycloaddition of diazoarylacetates and the danishefsky s diene stereoselective synthesis of 1 13 herbertenediol
Journal of Organic Chemistry, 2018Co-Authors: Qing Zhou, Fei Cao, Wendao Chu, Quanzhong LiuAbstract:Rodium chiral diene complex-catalyzed enantioselective cycloaddition of aryl α-diazoarylacetates and electron-enriched Danishefsky-type dienes afforded highly functionalized and optically enriched Cyclopentenones in excellent yields (up to 97% yield) and with good to excellent enantioselectivities (60-92% ee). (-)-1,13-Herbertenediol was successfully synthesized in an overall 25% yield employing the optically enriched Cyclopentenone with an all-carbon quaternary center as the key intermediate.
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Enantioselective Formal [4+1] Cycloaddition of Diazoarylacetates and the Danishefsky’s Diene: Stereoselective Synthesis of (−)-1,13-Herbertenediol
2018Co-Authors: Qing Zhou, Fei Cao, Wendao Chu, Quanzhong LiuAbstract:Rodium chiral diene complex-catalyzed enantioselective cycloaddition of aryl α-diazoarylacetates and electron-enriched Danishefsky-type dienes afforded highly functionalized and optically enriched Cyclopentenones in excellent yields (up to 97% yield) and with good to excellent enantioselectivities (60–92% ee). (−)-1,13-Herbertenediol was successfully synthesized in an overall 25% yield employing the optically enriched Cyclopentenone with an all-carbon quaternary center as the key intermediate
Steven D Jacob - One of the best experts on this subject based on the ideXlab platform.
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No Acid Required: 4π and 6π Electrocyclization Reactions of Dienyl Diketones for the Synthesis of Cyclopentenones and 2H‑Pyrans
2016Co-Authors: Steven D Jacob, Joshua L Brooks, Alison J FrontierAbstract:ABSTRACT: The 1,6-conjugate addition of nucleophiles to dienyl diketones produces either Cyclopentenone or 2H-pyran products with high selectivity through either Nazarov (4π) or 6π electrocyclization, respectively. The outcome of the reaction is dependent upon the nature of the nucleophile used. Nucleophiles that are anionic or easily deprotonated exclusively produce Cyclopentenones via Nazarov cyclization, whereas the neutral nucleophile DABCO promotes 6π cyclization to afford 2H-pyrans. Experimental evidence is presented for both retro-4π and-6π electrocyclization in these systems, lending support to the bifurcated mechanistic hypothesis proposed for these cyclizations. Electrocyclic reactions are becoming increasingly valuable in synthesis as chemists continue to develop new methods for catalyzing these cyclizations.1 In recent years, mild catalytic methods for achieving neutral,2 cationic,3 and anionic
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no acid required 4π and 6π electrocyclization reactions of dienyl diketones for the synthesis of Cyclopentenones and 2h pyrans
Journal of Organic Chemistry, 2014Co-Authors: Steven D Jacob, Joshua L Brooks, Alison J FrontierAbstract:The 1,6-conjugate addition of nucleophiles to dienyl diketones produces either Cyclopentenone or 2H-pyran products with high selectivity through either Nazarov (4π) or 6π electrocyclization, respectively. The outcome of the reaction is dependent upon the nature of the nucleophile used. Nucleophiles that are anionic or easily deprotonated exclusively produce Cyclopentenones via Nazarov cyclization, whereas the neutral nucleophile DABCO promotes 6π cyclization to afford 2H-pyrans. Experimental evidence is presented for both retro-4π and -6π electrocyclization in these systems, lending support to the bifurcated mechanistic hypothesis proposed for these cyclizations.
