TY - JOUR A1 - Linker, Torsten A1 - Engelhardt, Ulrike A1 - Sarkar, Arunkanti T1 - Kinetic resolution by Jacobsen epoxidation as an easy route to podophyllotoxin analoga Y1 - 2000 ER - TY - JOUR A1 - Linker, Torsten A1 - Linker, Ursula T1 - Einfache Synthese vierfach Acceptor-substituierter Alkene durch formale Dehydrodimerisierung von Malonsäureestern Y1 - 2000 ER - TY - JOUR A1 - Linker, Torsten A1 - Linker, Ursula T1 - Simple synthesis of tetra-acceptor-substituted alkenes by the formal dehydrodimerization of malonates Y1 - 2000 ER - TY - JOUR A1 - Linker, Torsten T1 - Radicals and Radical Reactions Y1 - 2000 ER - TY - JOUR A1 - Linker, Torsten T1 - Radikale in der Organischen Synthese Y1 - 2000 ER - TY - JOUR A1 - Linker, Torsten A1 - Engelhardt, Ulrike A1 - Sarkar, Arunkanti T1 - Cerium(IV) and other oxidizing agents Y1 - 2001 ER - TY - JOUR A1 - Sarodnick, Gerhard A1 - Linker, Torsten T1 - Quinoxalines X : a new and convenient synthesis of 1H-Pyrazolo[3,4-b] quinoxalines (Flavazoles) Y1 - 2001 ER - TY - JOUR A1 - Gyollai, Viktor A1 - Schanzenbach, Dirk A1 - Somsak, Laszlo A1 - Linker, Torsten T1 - Addition of malonyl radicals to glycals with C-1 acceptor groups: remarkable influence of the substituents on the product distribution Y1 - 2002 ER - TY - JOUR A1 - Linker, Torsten T1 - Selective reactions of transition-metal-generated radicals Y1 - 2002 ER - TY - JOUR A1 - Sarodnick, Gerhard A1 - Heydenreich, Matthias A1 - Linker, Torsten A1 - Kleinpeter, Erich T1 - Quinoxalines : Part 12: Synthesis and structural study of 1-(thiazol-2-yl)-1H-pyrazolo[3,4-b]quinoxalines - the dehydrogenative cyclization with hydroxylamine hydrochloride Y1 - 2003 ER - TY - JOUR A1 - Engelhardt, Ulrike A1 - Sarkar, Arunkanti A1 - Linker, Torsten T1 - Efficient Enantioselective Total Synthesis of (-)-Epipopdophyllotoxin Y1 - 2003 SN - 1433-7851 ER - TY - JOUR A1 - Vorndran, Katja Marianne A1 - Linker, Torsten T1 - Einfache zweistufige ipso-Substitution aromatischer Carbonsäuren durch Alkylhalogenide Y1 - 2003 ER - TY - JOUR A1 - Engelhardt, Ulrike A1 - Sarkar, Arunkanti A1 - Linker, Torsten T1 - Effiziente enantioselektive Totalsynthese von (-)-Epipodophyllotoxin Y1 - 2003 ER - TY - JOUR A1 - Vorndran, Katja Marianne A1 - Linker, Torsten T1 - Simpla Two-Step ipso Substitution of Aromatic Carboxylic Acids by Alkyl Halides Y1 - 2003 SN - 1433-7851 ER - TY - JOUR A1 - Grott, Saskia A1 - Peter, Martin G. A1 - Linker, Torsten A1 - Sefkow, Michael A1 - Kroll, Jürgen A1 - Koetz, Joachim A1 - Laschewsky, André A1 - Lokatis, Siegfried A1 - Rheinberg, Falko A1 - Manig, Yvette T1 - Portal = Chemie: Werkstoffe, Wirkstoffe, Lebensvorgänge BT - Die Potsdamer Universitätszeitung N2 - Aus dem Inhalt: - Chemie: Werkstoffe, Wirkstoffe, Lebensvorgänge - Institut für Kirchenrecht gegründet - Computerlinguisten erstellen digitales Wörterbuch - Vom Spaß am Graffiti-Sprayen T3 - Portal: Das Potsdamer Universitätsmagazin - 01-02/2003 Y1 - 2003 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-439713 SN - 1618-6893 IS - 01-02/2003 ER - TY - JOUR A1 - Peters, Karl A1 - Peters, E. M. A1 - Linker, Torsten T1 - Crystal structure of (1R,3S,5R)-3-hydroxy-2-methylene-6-oxabicyclo[3.2.1.]octan-7-one,C8H10O3 N2 - C8H10O3, orthorhombic, Pbca (no. 61), a = 10.592(3) Angstrom, b = 11.877(3) Angstrom, c = 36.833(9) Angstrom, V = 4633.6 Angstrom(3), Z = 24, R-gt(F) = 0.091, wR(ref)(F-2) = 0.219, T = 293 K. Y1 - 2004 SN - 1433-7266 ER - TY - JOUR A1 - Frohlich, L. A1 - Linker, Torsten T1 - Simple and diastereoselective synthesis of an A-ring precursor of dihydroxyvitamin D-3 (calcitriol) by photooxygenation N2 - A convenient synthesis of a racemic A-ring precursor of dihydroxyvitamin D-3 (calcitriol) is described. The key step involves the singlet oxygen ene reaction of the Lythgoe lactone, which proceeds with excellent regio- and good diastereoselectivities. Strong polar interactions are operative during the attack of O-1(2) to the double bond, which is important for the mechanism of such reactions Y1 - 2004 SN - 0936-5214 ER - TY - JOUR A1 - Hartmann, K. A1 - Kim, Boo Geun A1 - Linker, Torsten T1 - Manganese(III)-mediated radical reactions in carbohydrate chemistry : a new route to 3-deoxy-D-manno-oct-2- ulosonic acid (KDO) N2 - An acyclic alkene derived from a carbohydrate is employed as a substrate for manganese-mediated radical reactions for the first time. The addition of malonate is interesting for the mechanism of such reactions, whereas acetic acid as radical precursor affords lactones in excellent yield. The main diastereomer was easily separated and represents a key intermediate in the synthesis of KDO Y1 - 2004 SN - 0936-5214 ER - TY - JOUR A1 - Sommermann, T. A1 - Kim, Boo Geun A1 - Peters, Karl A1 - Peters, E. M. A1 - Linker, Torsten T1 - Short and stereoselective synthesis of C-glycosylated glycine derivatives from glycals by radical addition and reduction N2 - Only three steps are required for the convenient synthesis of 2-C-branched glyco-amino acids from glycals with good yields and stereoselectivities Y1 - 2004 SN - 1359-7345 ER - TY - JOUR A1 - Peters, Karl A1 - Peters, E. M. A1 - Rebien, F. A1 - Engelhardt, Ulrike A1 - Linker, Torsten T1 - Crystal structure of methyl (1R,4S)-4-hydroxy-1-phenyl-1,4-dihydronaphthalene-2-carboxylate,C18H16O3 N2 - C18H16O3, monoclinic, C12/c1 (no. 15), a = 28.674(4) Angstrom, b = 8.133(1) Angstrom, c = 13.065(2) Angstrom, beta = 108.96(1)degrees, V = 2881.6 Angstrom Z = 8, R-gt(F) = 0.077, wR(ref)(F-2) = 0.245, T = 293 K. Y1 - 2004 SN - 1433-7266 ER - TY - JOUR A1 - Peters, Karl A1 - Peters, E. M. A1 - Rebien, F. A1 - Maurer, M. A1 - Linker, Torsten T1 - Crystal structure of (3aS,4S,9R,9aS)-4-hydroxy-9-phenyl-3a,4,9,9a-tetra-hydro-3H-naphtho[2,3- c]furan-1- one,C18H16O3 N2 - C18H16O3, monoclinic, P12(1)/n1 (no. 14), a = 8.284(l) Angstrom, b = 9.524(l) Angstrom, c = 17.729(1) Angstrom, beta = 93.69(1)degrees, V = 1395.9 Angstrom(3), Z = 4, R-gt(F) = 0.052, wR(ref)(F-2) = 0.146, T = 293 K. Y1 - 2004 SN - 1433-7266 ER - TY - JOUR A1 - Kim, Boo Geun A1 - Schilde, Uwe A1 - Linker, Torsten T1 - New radical approaches to 3-deoxy-D-oct-2-ulosonic acids (KDO) N2 - Two different approaches. with an unsaturated carbohydrate as a radical acceptor and a carbohydrate derived aldehyde as a radical precursor, led to key intermediates in the synthesis of 3-deoxy-D-oct-2-ulosonic acids (KDO). Manganese(III) acetate and cerium(IV) ammonium nitrate were the reagents of choice for the oxidative generation of radicals, whereas samarium(II) iodide was employed for reductive couplings. Both strategies were realized by using easily available starting materials, with acetic acid as C-2 and ethyl acrylate as C-3 building blocks, respectively Y1 - 2005 SN - 0039-7881 ER - TY - JOUR A1 - Peters, Karl A1 - Peters, E. M. A1 - Kim, Boo Geun A1 - Linker, Torsten T1 - Crystal structure of ethyl (3aR,4R,5R,6R,7aR)-4,5-diacetoxy-6-acetoxymethyl-2-oxy-3a,5,6,7a-tetrahy dro-4H- pyrano[3,2-d]isoxazole-3-carboxylate, C16H21NO11 N2 - C16H21NO11, monoclinic, P12(1)1 (no. 4), a = 8.181(1) angstrom, b = 11.604(2) angstrom, c = 10.193(1) angstrom, beta = 101.59(1)degrees, V = 947.9 angstrom(3), Z = 2, R-gt(F) = 0.068, wR(ref)(F-2) = 0.177, T = 293 K. Y1 - 2005 SN - 1433-7266 ER - TY - JOUR A1 - Peters, Karl A1 - Peters, E. M. A1 - Linker, Ursula A1 - Linker, Torsten T1 - Crystal structure of 1,1,2,2-tetramethoxycarbonylethanol, C2H(CH3OCO)(4)OH N2 - C10H14O9, monoclinic, C12/c1 (no. 15), a = 15.801(1) angstrom, b = 7.920(1) angstrom, c = 21.055(2) angstrom, beta = 101.31 (1)degrees, V = 2583.8 angstrom(3), Z = 8, R-gt(F) 0.044, wR(ref)(F-2) = 0.134, T = 293 K. Y1 - 2005 SN - 1433-7266 ER - TY - JOUR A1 - Peters, Karl A1 - Peters, E. M. A1 - Rebien, F. A1 - Linker, Torsten T1 - Crystal structure of methyl (1R,2S,3R,4S)-1-phenyl-3,4-epoxi-1,2,3,4-tetrahydronaphthalene-2-carboxy late,C18H16O3 N2 - C18H16O3, monoclinic, P12(1)/c1 (no. 14), a = 14.954(3) angstrom, b = 8.088(2) angstrom, c = 11.973(2) angstrom, beta = 93.50(1)degrees, V = 1445.4 angstrom(3), Z = 4, R-gt(F) = 0.083, wR(ref)(F-2) = 0.249, T = 293 K. Y1 - 2005 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 - TY - JOUR A1 - Fudickar, Werner A1 - Fery, Andreas A1 - Linker, Torsten T1 - Reversible light and air-driven lithography by singlet oxygen Y1 - 2005 SN - 0002-7863 ER - TY - JOUR A1 - Fudickar, Werner A1 - Linker, Torsten T1 - Imaging by sensitized oxygenations of photochromic anthracene films BT - Examination of effects that improve performance and reversibility JF - Chemistry - a European journal N2 - The aliphatic anthracene compound 1 and the oligomeric anthracene 2 were synthesized. Thin films of 1 and 2 mixed with the sensitizers tetraphenylporphyrin (TPP) and methylene blue (MB) were irradiated with visible light in air. Upon formation of singlet oxygen, the anthracene units were converted quantitatively to the corresponding endoperoxides. Heating of the irradiated samples afforded the parent anthracenes with high yields. Here, we demonstrate that the kinetics and reversibility of this reaction strongly depend on the microenvironment of the anthracene groups in the two compounds. The photooxidation of thin films of I is accompanied by interesting changes in the morphology of the film and allows the first application of 1 as a nondestructive negative-tone photo-resist for lithography and as an oxidizing ink. The morphology of 2 remained unchanged after photooxidation as a result of the stabilizing oligomer backbone. This stabilizing effect significantly improves the photochromic performance of 2. The reversibility of the photooxidation is very high (> 90%) for oligomeric films of 2 after several cycles of irradiation and beating. Decomposition of the anthracene and a loss of the activity of the sensitizer diminish slightly the performance of the monomeric species. KW - anthracenes KW - lithography KW - photochromism KW - singlet oxygen KW - thin films Y1 - 2006 U6 - https://doi.org/10.1002/chem.200600387 SN - 0947-6539 VL - 12 SP - 9276 EP - 9283 PB - WILEY‐VCH CY - Weinheim ER - TY - JOUR A1 - Fudickar, Werner A1 - Vomdran, Katja A1 - Linker, Torsten T1 - Auxiliary controlled singlet-oxygen ene reactions of cyclohexenes JF - Tetrahedron N2 - The photooxygenation of homochiral cyclohexene ketals, which are easily available from 2-cyclohexenone and L-tartrates, affords hydroperoxides and after reduction the corresponding allylic alcohols in good yields and high regioselectivities. This can be rationalized by electronic repulsions in a perepoxide intermediate and provides evidence for unfavorable 1,3 diaxial interactions with a dioxolane oxygen atom. Only low stereoselectivities were observed, due to the flexibility of the cyclohexene ring. However, the diastereomers could be separated and after cleavage of the auxiliary, 4-hydroxy-2-cyclohexen-1-one was isolated in enantiomerically pure form, which can serve as a building block for natural product synthesis. KW - singlet oxygen KW - auxiliary control KW - regioselectivity KW - stereoselectivity Y1 - 2006 U6 - https://doi.org/10.1016/j.tet.2006.07.104 SN - 0040-4020 VL - 62 IS - 46 SP - 10639 EP - 10646 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Zehm, Daniel A1 - Fudickar, Werner A1 - Hans, Melanie A1 - Schilde, Uwe A1 - Kelling, Alexandra A1 - Linker, Torsten T1 - 9,10-Diarylanthracenes as molecular switches : syntheses, properties, isomerisations and their reactions with singlet oxygen N2 - A series of 9,10-diarylanthracenes with various substituents at the ortho positions have been synthesised by palladium-catalysed cross-coupling reactions. Such compounds exhibit interesting physical properties and can be applied as molecular switches. Despite the high steric demand of the substituents, products were formed in moderate-to-good yields. In some cases, microwave conditions further improved yields. Bis-coupling afforded two isomers (syn and anti) that do not interconvert at room temperature. These products were easily separated and their relative stereochemistries were unequivocally assigned by NMR spectroscopy and X-ray analysis. The syn and anti isomers exhibit different physical properties (e.g., melting points and solubilities) and interconversion by rotation around the aryl-aryl axis commences at <100 °C for fluoro-substituted diarylanthracenes and at >300 °C for alkyl- or alkoxy-substituted diarylanthracenes. The reactions with singlet oxygen were studied separately and revealed different reactivities and reaction pathways. The yields and reactivities depend on the size and electronic nature of the substituents. The anti isomers form the same 9,10-endoperoxides as the syn species, occasionally accompanied by unexpected 1,4-endoperoxides as byproducts. Thermolysis of the endoperoxides exclusively yielded the syn isomers. The interesting rotation around the aryl-aryl axis allows the application of 9,10-diarylanthracenes as molecular switches, which are triggered by light and air under mild conditions. Finally, the oxygenation and thermolysis sequence provides a simple, synthetic access to a single stereoisomer (syn) from an unselective coupling step. Y1 - 2008 SN - 0947-6539 ER - TY - JOUR A1 - Krüger, Tobias A1 - Vorndran, Katja A1 - Linker, Torsten T1 - Regioselective arene functionalization : simple substitution of carboxylate by alkyl groups N2 - Arenes with various alkyl side-chains were synthesized in high yields and excellent regioselectivities. Starting from toluic and naphthoic acids, the carboxylate group was conveniently substituted by alkyl halides by Birch reduction and subsequent decarbonylation. The method is characterized by inexpensive starting materials and reagents, and methylation of arenes was realized. Besides simple alkyl substituents, the scope of arene functionalization was extended by benzyl, fluoro, amino, and ester groups. We were able to control the alkylation of 1-naphthoic acid during Birch reduction by the addition of tert-butanol. This allowed the regioselective synthesis of mono and bis-substituted naphthalenes from the same starting material. Y1 - 2009 UR - http://www3.interscience.wiley.com/cgi-bin/jhome/26293/ U6 - https://doi.org/10.1002/chem.200901774 SN - 0947-6539 ER - TY - JOUR A1 - Sarodnick, Gerhard A1 - Linker, Torsten A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Starke, Ines A1 - Fürstenberg, Sylvia A1 - Kleinpeter, Erich T1 - Quinoxalines XV : convenient synthesis and structural study of pyrazolo[1,5-alpha]quinoxalines N2 - A series of aryloxymethylquinoxaline oximes, hitherto unknown and synthesized from the corresponding aldehydes, afforded in only one step pyrazolo[1,5-;]quinoxalines in the presence of acetic anhydride at high temperatures. A formal [3,5]-sigmatropic rearrangement was proposed as the mechanistic rationale for this unprecedented transformation. Saponification with potassium hydroxide furnished the free phenol derivatives which were studied by NMR spectroscopy and accompanying theoretical DFT calculations, establishing intramolecular hydrogen bonding and the spatial magnetic properties. Additionally, mass spectrometric fragmentation was investigated by B/E-linked scans and collision-induced dissociation experiments. The fragmentation pattern devoted a new gas phase rearrangement process, which proved to be unique and characteristic for pyrazolo[1,5-;]quinoxalines. Y1 - 2009 UR - http://pubs.acs.org/journal/joceah U6 - https://doi.org/10.1021/Jo802398g SN - 0022-3263 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 - Fudickar, Werner A1 - Linker, Torsten T1 - Photoimaging with singlet oxygen at the solid-air interface N2 - Films of anthracene carboxylic acids were irradiated through photomasks and oxidized at the exposed regions by singlet oxygen upon sensitization. The efficiency of a photomask to protect the material underneath was investigated by optical and infrared spectroscopy. As the thickness of the film is reduced, the efficiency of the mask drops. This is explained by the migration of singlet oxygen at the solid-air interface, which in turn reacts at the masked area. For films with a thickness of < 15 nm, the efficiency of the mask approaches zero: sufficient efficiency is achieved at thicknesses > 100 nm. From the investigations, it will become clear that the contrast between the irradiated and masked area of an image is affected by reduction of the film thickness. On the other hand, the resolution of an image, which relates to the minimum feature size of an image, is not dependent on the thickness of the film. The contributions of "inside" and "outside" reactions are examined separately, and it quantitative approximation of the spatial range of both modes of the oxygenation is given. We set tip an approximate relation between mask efficiency and experimental conditions comprising internal and external oxygen diffusion, film thickness, and mask dimensions. These results give it deeper insight into the limits of resolution and contrast in singlet oxygen lithography. Y1 - 2009 UR - http://pubs.acs.org/journal/langd5 U6 - https://doi.org/10.1021/La9008976 SN - 0743-7463 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 - THES A1 - Elamparuthi, Elangovan A1 - Linker, Torsten A1 - Kelling, Alexandra A1 - Schilde, Uwe T1 - Crystal structure of methyl 3,4,6-tri-O-benzyl-2-deoxy-2-C-nitromethyl-beta-D-galactopyranoside, C29H33NO7 Y1 - 2009 UR - http://www.oldenbourg.de/verlag/zkristallogr/mn-ncsc.htm U6 - https://doi.org/10.1524/ncrs.2009.0054 SN - 1433-7266 ER - TY - JOUR A1 - Yin, Jian A1 - Linker, Torsten T1 - Convenient synthesis of bicyclic carbohydrate 1,2-lactones and their stereoselective opening to 1- functionalized glucose derivatives N2 - Closed and re-opened for business: C-2 branched carbohydrates 1 cyclize under conditions of decarboxylation to the hitherto unknown carbohydrate 1,2-lactones 2 in high yields. The gluco isomer can be opened at the anomeric position with various nuceophiles in the presence of Sc(OTf)3, which allows the stereoselective synthesis of 1-functionalized glucose derivatives 3. Thus, 1,2-bis-C-branched saccharides become available in only a few steps starting from glycals. Y1 - 2009 UR - http://www3.interscience.wiley.com/cgi-bin/jhome/26293/ U6 - https://doi.org/10.1002/chem.200802178 SN - 0947-6539 ER - TY - JOUR A1 - Yin, Jian A1 - Linker, Torsten T1 - Stereodivergent syntheses at the glucose backbone N2 - Both diastereomers of 2-C-branched carbohydrates with various functional groups are selectively available from the same malonate precursor in good yields in only a few steps. Y1 - 2009 UR - http://www.rsc.org/Publishing/Journals/OB/index.asp U6 - https://doi.org/10.1039/B918893m SN - 1477-0520 ER - TY - JOUR A1 - Fudickar, Werner A1 - Linker, Torsten T1 - Novel anthracene materials for applications in lithography and reversible photoswitching by light and air N2 - Herein we demonstrate how the photoreaction between anthracenes and singlet oxygen (O-1(2)) is employed for applications either as photoswitch or as photoresist. Thin Films of the diaryl-alkyl anthracene 1 and the analogous oligomeric species 2 were it-radiated under photomasks to generate pattern structures composed of 1/1-O-2 and 2/2-O-2. Kelvin probe force microscopy (KPFM) provided a powerful and nondestructive method to image the pattern information. The following studies based on AFM, KPFM and contact angle measurements unfold that the two species 1 and 2 underwent different progressions after the imaging step. Degrading is observed for the monomeric compound 1 and the pattern eventually becomes recognizable in topography. In the oxidized state (1-O-2) the monomeric species remains physically stable. In consequence, the unreacted portion is removable and the remaining oxygenated form 1-O-2 is sufficiently stable to protect in underlying substrate (e.g., silver) from etching. Thus, the system 1/1-O-2 operates as photoresist. Oil the other hand, both states of the oligomier 2 remain stable. The Film is stable up to temperatures > 120 degrees C required to erase the pattern within acceptable time by cycloreversion. Anthracene 2 therefore acts as erasable and rewritable photochromic switch. The different behavior between 1 and 2 is explained by phase transitions which cause crystallization and finally ablation. Such transitions affect only the monomeric system 1/1-O-2 and not the oligomeric system 2/2-O-2. In conclusion, we designed two very similar materials based on diarylanthracenes, which can act either as a photoresist or as a rewritable photochrornic switch. Y1 - 2010 UR - http://pubs.acs.org/journal/langd5 U6 - https://doi.org/10.1021/La904299n SN - 0743-7463 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 - Fudickar, Werner A1 - Linker, Torsten T1 - Reversible Photooxygenation of Alkynylanthracenes chemical generation of singlet oxygen under very mild conditions JF - Chemistry - a European journal KW - anthracenes KW - oxidation KW - peroxides KW - reversibility KW - singlet oxygen Y1 - 2011 U6 - https://doi.org/10.1002/chem.201102230 SN - 0947-6539 VL - 17 IS - 49 SP - 13661 EP - 13664 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Yin, Jian A1 - Linker, Torsten T1 - Stereoselective diversity-oriented syntheses of functionalized saccharides from bicyclic carbohydrate 1,2-lactones JF - Tetrahedron N2 - Bicyclic carbohydrate 1,2-lactones have been synthesized in only two steps and high yields by saponification and subsequent cyclization from known malonate addition products to glycals. The gluco-configured lactone serves as an important precursor for diversity-oriented syntheses. Thus, stereoselective opening of the lactone ring was realized with various nucleophiles in the presence of Sc(OTf)(3). This enabled the introduction of different substituents at the anomeric position, to afford a broad variety of 1-functionalized carbohydrates. On the other hand, stereoselective alpha-substitution of the gluco-configured lactone with different electrophiles and subsequent ring opening gives a collection of 2-functionalized saccharides. More than 30 products have been isolated in analytically pure form, and their configurations were unequivocally established by various NMR methods. Thus, carbohydrate 1,2-lactones are attractive precursors for the stereoselective synthesis of diverse saccharides. KW - Carbohydrates KW - Lactones KW - Glycosides KW - Molecular diversity KW - Synthetic methods Y1 - 2011 U6 - https://doi.org/10.1016/j.tet.2011.01.069 SN - 0040-4020 VL - 67 IS - 13 SP - 2447 EP - 2461 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Vidadala, Srinivasa Rao A1 - Pimpalpalle, Tukaram M. A1 - Linker, Torsten A1 - Hotha, Srinivas T1 - Gold-Catalyzed reactions of 2-C-Branched carbohydrates mild glycosidations and selective anomerizations JF - European journal of organic chemistry N2 - 2-C-branched methyl glycosides react with various alcohols under gold catalysis to transglycosylated products. The method is applicable for the convenient synthesis of disaccharides. Without nucleophile a selective anomerization occurs, giving first access to alpha-configured 2-C-nitromethyl glycosides. The results are interesting for the mechanism of gold-catalyzed glycosidations. KW - Anomerization KW - Carbohydrates KW - Glycosidation KW - Gold KW - Synthetic methods Y1 - 2011 U6 - https://doi.org/10.1002/ejoc.201100134 SN - 1434-193X IS - 13 SP - 2426 EP - 2430 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Pimpalpalle, Tukaram M. A1 - Vidadala, Srinivasa Rao A1 - Hotha, Srinivas A1 - Linker, Torsten T1 - Lewis acid-catalyzed stereoselective lactonization and subsequent glycosidation of 2-C-malonyl carbohydrates JF - Chemical communications N2 - Gold(III) bromide is a suitable catalyst for the stereoselective cyclization of 2-C-malonyl carbohydrates to the anomeric center under retention of one ester group. Reopening of the lactones with alcohols in the presence of TMSOTf affords allyl, propargyl and benzyl glycosides with high alpha-selectivity. Y1 - 2011 U6 - https://doi.org/10.1039/c1cc13425f SN - 1359-7345 VL - 47 IS - 37 SP - 10434 EP - 10436 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Linker, Torsten T1 - Synthesis and NMR spectroscopic conformational analysis of esters of 4-hydroxy-cyclohexanone-the more polar the molecule the more stable the axial conformer N2 - The esters of 4-hydroxy-cyclohexanone and a series of carboxylic acids R-COOH with R of different electronic and steric influence (R=Me, Et, n-Pr, i-Pr, n-Bu, i-Bu, sec-Bu, t-Bu, CF3, CH2Cl, CHCl2, CCl3, CH2Br, CHBr2, and CBr3) were synthesized and the conformational equilibria studied by 1H and 13C NMR spectroscopy at 103 K and at 295 K, respectively. The geometry of optimized structures of the axial/equatorial chair conformers was computed at the ab initio MO and DFT levels of theory. Only one preferred conformation was obtained for the axial and the equatorial conformer as well. When comparing the conformational equilibria of the cyclohexanone esters with those of the corresponding cyclohexyl esters a certain polarity contribution of the cyclohexanone framework was revealed, which is independent of the substituent effects and increases the stability of the axial conformers by a constant amount. Y1 - 2012 SN - 0040-4020 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Linker, Torsten T1 - Synthesis and NMR spectroscopic conformational analysis of esters of 4-hydroxy-cyclohexanone-the more polar the molecule the more stable the axial conformer JF - Tetrahedron N2 - The esters of 4-hydroxy-cyclohexanone and a series of carboxylic acids R-COOH with R of different electronic and steric influence (R=Me, Et, n-Pr, i-Pr, n-Bu, i-Bu, sec-Bu, t-Bu, CF3, CH2Cl, CHCl2, CCl3, CH2Br, CHBr2, and CBr3) were synthesized and the conformational equilibria studied by H-1 and C-13 NMR spectroscopy at 103 K and at 295 K, respectively. The geometry of optimized structures of the axial 'equatorial chair conformers was computed at the ab initio MO and DFT levels of theory. Only one preferred conformation was obtained for the axial and the equatorial conformer as well. When comparing the conformational equilibria of the cyclohexanone esters with those of the corresponding cyclohexyl esters a certain polarity contribution of the cyclohexanone framework was revealed, which is independent of the substituent effects and increases the stability of the axial conformers by a constant amount. KW - 4-Substituted cyclohexanones KW - Conformational analysis KW - Dynamic NMR KW - Simulation of H-1 NMR spectra KW - Quantum chemical calculations KW - ALTONA equation Y1 - 2012 U6 - https://doi.org/10.1016/j.tet.2012.01.022 SN - 0040-4020 VL - 68 IS - 10 SP - 2363 EP - 2373 PB - Elsevier CY - Oxford 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 - Pimpalpalle, Tukaram M. A1 - Yin, Jian A1 - Linker, Torsten T1 - Barton radical reactions of 2-C-branched carbohydrates JF - Organic & biomolecular chemistry : an international journal of synthetic, physical and biomolecular organic chemistry N2 - Barton esters have been introduced into the side chain of carbohydrates with high yields in only a few steps from easily available glycals. Their radical reactions afford 2-C-methyl and 2-C-bromomethyl hexoses, pentoses and disaccharides in good yields in analytically pure form. Since the Barton esters have been synthesized by an oxidative radical addition and their transformations by reductive radical processes, our results demonstrate the power of such reactions in carbohydrate chemistry. Y1 - 2012 U6 - https://doi.org/10.1039/c1ob06370g SN - 1477-0520 VL - 10 IS - 1 SP - 103 EP - 109 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Fudickar, Werner A1 - Linker, Torsten T1 - Why triple bonds protect acenes from oxidation and decomposition JF - Journal of the American Chemical Society N2 - An experimental and computational study on the impact of functional groups on the oxidation stability of higher acenes is presented. We synthesized anthracenes, tetracenes, and pentacenes with various substituents at the periphery, identified their photooxygenation products, and measured the kinetics. Furthermore, the products obtained from thermolysis and the kinetics of the thermolysis are investigated. Density functional theory is applied in order to predict reaction energies, frontier molecular orbital interactions, and radical stabilization energies. The combined results allow us to describe the mechanisms of the oxidations and the subsequent thermolysis. We found that the alkynyl group not only enhances the oxidation stability of acenes but also protects the resulting endoperoxides from thermal decomposition. Additionally, such substituents increase the regioselectivity of the photooxygenation of tetracenes and pentacenes. For the first time, we oxidized alkynylpentacenes by using chemically generated singlet oxygen (O-1(2)) without irradiation and identified a 6,13-endoperoxide as the sole regioisomer. The bimolecular rate constant of this oxidation amounts to only 1 X 10(5) s(-1) M-1. This unexpectedly slow reaction is a result of a physical deactivation of O-1(2). In contrast to unsubstituted or aryl-substituted acenes, photooxygenation of alkynyl-substituted acenes proceeds most likely by a concerted mechanism, while the thermolysis is well explained by the formation of radical intermediates. Our results should be important for the future design of oxidation stable acene-based semiconductors. Y1 - 2012 U6 - https://doi.org/10.1021/ja306056x SN - 0002-7863 VL - 134 IS - 36 SP - 15071 EP - 15082 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Yin, Jian A1 - Linker, Torsten T1 - Recent advances in the stereoselective synthesis of carbohydrate 2-C-analogs JF - Organic & biomolecular chemistry : an international journal of synthetic, physical and biomolecular organic chemistry N2 - C-branched carbohydrates are of current interest for glycochemistry, are widely found in nature and serve as important subunits in many antibiotics, bacterial polysaccharides and macrolides. Among C-functionalized saccharides, 2-C-branched carbohydrates represent challenging structures for synthetic chemists, since in contrast to C-glycosides they are not easily accessible from glycosyl bromides or other simple precursors. In this perspective we want to summarize recent approaches to 2-C-branched carbohydrates over the past fifteen years. The two main strategies are based on ring-opening of 1,2-cyclopropanated carbohydrates by various reagents, as well as radical additions to glycals and further transformations, developed in our group. Both methods are characterized by high stereoselectivities and good yields and give access to a broad variety of functionalized carbohydrate 2-C-analogs. Y1 - 2012 U6 - https://doi.org/10.1039/c2ob06529k SN - 1477-0520 VL - 10 IS - 12 SP - 2351 EP - 2362 PB - Royal Society of Chemistry CY - Cambridge ER -