TY - JOUR A1 - Anklam, Elke A1 - Behler, Jörg A1 - Dingermann, Theodor A1 - Elsinghorst, Paul A1 - Fischer, Jochen A1 - Esselen, Melanie A1 - Foerster, Christian A1 - Fröhlich, Daniel A1 - Goedel, Werner Andreas A1 - Gregory, Peter A1 - Grimme, Stefan A1 - Hackenberger, Christian A1 - Hansmann, Max A1 - Heppekausen, Johannes A1 - Hasenstab-Riedel, Sebastian A1 - Kirchhoff, Erhard A1 - Kratz, Karl-Ludwig A1 - Krausz, Ferenc A1 - Linker, Torsten A1 - List, Benjamin A1 - Ray, Kallol A1 - Salzer, Reiner A1 - Schubert, Ulrich A1 - Schueth, Ferdi A1 - Schwarz, Helmut A1 - Schwietzke, Uta A1 - Strey, Reinhard A1 - Stumpf, Thorsten A1 - Vaagt, Franziska A1 - Volodkin, Dmitry A1 - Wilke, Guenther A1 - Zass, Engelbert A1 - Zemb, Thomas T1 - Awards JF - Nachrichten aus der Chemie : Zeitschrift der Gesellschaft Deutscher Chemiker Y1 - 2013 U6 - https://doi.org/10.1002/nadc.201390372 SN - 1439-9598 SN - 1868-0054 VL - 61 IS - 11 SP - 1145 EP - 1148 PB - Ges. Dt. Chemiker CY - Frankfurt, Main ER - TY - JOUR A1 - Bauch, Marcel A1 - Böttcher, Dominique A1 - Bornscheuer, Uwe T. A1 - Linker, Torsten T1 - Enzymatic Cleavage of Aryl Acetates JF - ChemCatChem : heterogeneous & homogeneous & bio- & nano-catalysis ; a journal of ChemPubSoc Europe N2 - Seven enzymes have been screened for the cleavage of aryl acetates. Phenyl and naphthyl acetates react with lipases and esterases, whereas the sterically demanding anthracene acetate gave a conversion only with porcine liver esterase and esterase 2 from Bacillus subtilis (BS2). These two enzymes have been employed on a preparative (0.5 mmol) scale and afforded cleavage products in 91 and 94% yields, even for anthracene acetate. Thus, this method is superior to chemical cleavage with catalytic amounts of sodium methoxide (Zemplen conditions), which gave only low conversions. Finally, regioselectivity has been achieved with an anthracene bisacetate, in which an ethyl group controls the cleavage of the first acetate. This indicates that steric interactions play a crucial role in the enzymatic cleavage of aryl acetates, which might be interesting for future applications or the development of enzyme inhibitors. KW - arenes KW - enzyme catalysis KW - regioselectivity KW - steric hindrance KW - substituent effects Y1 - 2016 U6 - https://doi.org/10.1002/cctc.201600678 SN - 1867-3880 SN - 1867-3899 VL - 8 SP - 2853 EP - 2857 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Bauch, Marcel A1 - Fudickar, Werner A1 - Linker, Torsten T1 - Stereoselective [4+2] Cycloaddition of Singlet Oxygen to Naphthalenes Controlled by Carbohydrates JF - Molecules : a journal of synthetic chemistry and natural product chemistry N2 - Stereoselective reactions of singlet oxygen are of current interest. Since enantioselective photooxygenations have not been realized efficiently, auxiliary control is an attractive alternative. However, the obtained peroxides are often too labile for isolation or further transformations into enantiomerically pure products. Herein, we describe the oxidation of naphthalenes by singlet oxygen, where the face selectivity is controlled by carbohydrates for the first time. The synthesis of the precursors is easily achieved starting from naphthoquinone and a protected glucose derivative in only two steps. Photooxygenations proceed smoothly at low temperature, and we detected the corresponding endoperoxides as sole products by NMR. They are labile and can thermally react back to the parent naphthalenes and singlet oxygen. However, we could isolate and characterize two enantiomerically pure peroxides, which are sufficiently stable at room temperature. An interesting influence of substituents on the stereoselectivities of the photooxygenations has been found, ranging from 51:49 to up to 91:9 dr (diastereomeric ratio). We explain this by a hindered rotation of the carbohydrate substituents, substantiated by a combination of NOESY measurements and theoretical calculations. Finally, we could transfer the chiral information from a pure endoperoxide to an epoxide, which was isolated after cleavage of the sugar chiral auxiliary in enantiomerically pure form. KW - singlet oxygen KW - photooxygenation KW - naphthalenes KW - carbohydrates KW - stereoselectivity KW - auxiliary control KW - [4+2] cycloaddition Y1 - 2021 U6 - https://doi.org/10.3390/molecules26040804 SN - 1420-3049 VL - 16 IS - 4 PB - MDPI CY - Basel ER - TY - JOUR A1 - Bauch, Marcel A1 - Klaper, Matthias A1 - Linker, Torsten T1 - Intermediates in the cleavage of endoperoxides JF - Journal of physical organic chemistry N2 - The decomposition of anthracene endoperoxides has been investigated under various conditions. Thermolyses proceed via radical intermediates and afford anthracenes and rearrangement products, depending on the substitution pattern. Interestingly, not only the O-O but also the C-O bond can be cleaved homolytically. Under basic conditions fragmentations take place, affording anthraquinone, and reactive oxygen species. This mechanism explains the often observed decomposition of endoperoxides during work-up. Finally, an acid-catalyzed cleavage has been observed under release of hydrogen peroxide. The results should be interesting for the mechanistic understanding of peroxide decomposition and the endoperoxides might serve as mild sources of reactive oxygen species for future applications. Copyright (C) 2016 John Wiley & Sons, Ltd. KW - peroxides KW - radicals KW - reaction mechanism KW - reactive intermediates Y1 - 2017 U6 - https://doi.org/10.1002/poc.3607 SN - 0894-3230 SN - 1099-1395 VL - 30 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Bauch, Marcel A1 - Krtitschka, Angela A1 - Linker, Torsten T1 - Photooxygenation of oxygen-substituted naphthalenes JF - Journal of physical organic chemistry N2 - The reaction of oxygen-substituted naphthalenes with singlet oxygen (O-1(2)) has been investigated, and labile endoperoxides have been isolated and characterized at -78 degrees C for the first time. Low-temperature kinetics by UV spectroscopy revealed that alkoxy and silyloxy substituents remarkably increase the rate of photooxygenations compared to 1,4-dimethylnaphthalene, whereas acyloxy-substituted acenes are inert towards O-1(2). The reactivities nicely correlate with HOMO energies and free activation energies, which we determined by density functional theory calculations. The lability of the isolated endoperoxides is due to their very fast back reaction to the corresponding naphthalenes even at -20 degrees C under release of O-1(2), making them to superior sources of this reactive species under very mild conditions. Finally, a carbohydrate-substituted naphthalene has been synthesized, which reacts reversibly with O-1(2) and might be applied for enantioselective oxidations in future work. KW - kinetics KW - labile peroxides KW - low-temperature experiments KW - naphthalenes KW - singlet oxygen Y1 - 2017 U6 - https://doi.org/10.1002/poc.3734 SN - 0894-3230 SN - 1099-1395 VL - 30 SP - 6803 EP - 6813 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Bramborg, Andrea A1 - Linker, Torsten T1 - Selective synthesis of 1,4-dialkylbenzenes from terephthalic acid N2 - Terephthalic acid reacts with alkyl halides under Birch conditions to substituted 1,4-cyclohexadienes in high yields and good stereoselectivities. Electrophiles containing ester or nitrile groups undergo a surprising fragmentation under the reaction conditions. Subsequent treatment with chlorosulfonic acid proceeds by an interesting tandem decarbonylation/decarboxylation, affording 1,4-dialkylbenzenes in excellent regioselectivity. Thus our new method is superior to classical Friedel-Crafts alkylations. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/jhome/77002176 U6 - https://doi.org/10.1002/adsc.201000322 SN - 1615-4150 ER - TY - JOUR A1 - Bramborg, Andrea A1 - Linker, Torsten T1 - Regioselective synthesis of alkylarenes by two-step ipso-substitution of aromatic dicarboxylic acids JF - European journal of organic chemistry N2 - A strategy for the regioselective alkylation of arenes was developed, starting from commercially available and inexpensive terephthalic acid or naphthalene-1,4-dicarboxylic acid. The method entails a formal ipso-substitution of the carboxylate groups by a sequence of reductive alkylation under Birch conditions and subsequent acid-mediated rearomatization with loss of carbon monoxide and carbon dioxide. More than 20 different arenes with various side-chains were synthesized. With naphthalene-1,4-dicarboxylic acid as starting material, we were able to control the degree of alkylation by choosing the appropriate electrophile in the Birch reduction. Thus, bisalkylated naphthalenes and naphthoic acids became available chemoselectively. All reactions afforded a single regioisomer exclusively in high yields. Overall, aromatic dicarboxylic acids are suitable substrates for a two-step ipso-substitution that allows the selective synthesis of alkylated benzenes and naphthalenes. KW - Synthetic methods KW - Alkylation KW - Birch reduction KW - Arenes KW - Regioselectivity Y1 - 2012 U6 - https://doi.org/10.1002/ejoc.201200823 SN - 1434-193X IS - 28 SP - 5552 EP - 5563 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Elamparuthi, Elangovan A1 - Linker, Torsten T1 - Carbohydrate-2-deoxy-2-phosphonates : simple synthesis and Horner-Emmons reaction N2 - Phosphorus meets carbohydrates: Dimethyl phosphite reacts with ceric(IV) ammonium nitrate (CAN) to give phosphonyl radicals that add to glycals 1. The derivatives 2 were isolated in high yields and during a subsequent Horner-Emmons reaction underwent an interesting elimination to give 3,6-dihydro-2H-pyrans 3. The short sequence with simple precursors is applicable to the transformation of hexoses, pentoses, and disaccharides. Bn=benzyl. Y1 - 2009 UR - http://onlinelibrary.wiley.com/journal/10.1002/(28ISSN)291521-3773 U6 - https://doi.org/10.1002/anie.200804725 SN - 1433-7851 ER - TY - JOUR A1 - Elamparuthi, Elangovan A1 - Linker, Torsten A1 - Kelling, Alexandra A1 - Schilde, Uwe T1 - Crystal structure of methyl 3,4-di-O-benzyl-2-deoxy-2-C-nitromethyl-alpha-D-arabinopyranoside, C21H25NO6 Y1 - 2009 UR - http://www.oldenbourg.de/verlag/zkristallogr/mn-ncsc.htm U6 - https://doi.org/10.1524/ncrs.2009.0027 SN - 1433-7266 ER - TY - JOUR A1 - Engelhardt, Ulrike A1 - Linker, Torsten T1 - 1,4-cyclohexadienes as mechanistic probes for the Jacobsen epoxidation : evidence for radical pathways N2 - 1,4-Cyclohexadienes allow a direct comparison of epoxidation and C - H oxidation within the same molecule and give evidence for radical pathways during the Jacobsen epoxidation Y1 - 2005 ER -