@article{FudickarMetzMaiLindeetal.2021, author = {Fudickar, Werner and Metz, Melanie and Mai-Linde, Yasemin and Kr{\"u}ger, Tobias and Kelling, Alexandra and Sperlich, Eric and Linker, Torsten}, title = {Influence of functional groups on the ene reaction of singlet oxygen with 1,4-cyclohexadienes}, series = {Photochemistry and photobiology : the official journal of the American Society for Photobiology}, volume = {97}, journal = {Photochemistry and photobiology : the official journal of the American Society for Photobiology}, number = {6}, publisher = {Wiley}, address = {Malden, Mass.}, issn = {0031-8655}, doi = {10.1111/php.13422}, pages = {1289 -- 1297}, year = {2021}, abstract = {The photooxygenation of 1,4-cyclohexadienes has been studied with a special focus on regio- and stereoselectivities. In all examples, only the methyl-substituted double bond undergoes an ene reaction with singlet oxygen, to afford hydroperoxides in moderate to good yields. We explain the high regioselectivities by a "large-group effect" of the adjacent quaternary stereocenter. Nitriles decrease the reactivity of singlet oxygen, presumably by quenching, but can stabilize proposed per-epoxide intermediates by polar interactions resulting in different stereoselectivities. Spiro lactams and lactones show an interesting effect on regio- and stereoselectivities of the ene reactions. Thus, singlet oxygen attacks the double bond preferentially anti to the carbonyl group, affording only one regioisomeric hydroperoxide. If the reaction occurs from the opposite face, the other regioisomer is exclusively formed by severe electrostatic repulsion in a perepoxide intermediate. We explain this unusual behavior by the fixed geometry of spiro compounds and call it a "spiro effect" in singlet oxygen ene reactions.}, language = {en} } @article{WessigFreyseSchusteretal.2020, author = {Wessig, Pablo and Freyse, Daniel and Schuster, David and Kelling, Alexandra}, title = {Fluorescent dyes with large stokes shifts based on Benzo[1,2-d:4,5-d']bis([1,3]dithiole) ("S4-DBD Dyes")}, series = {Europan journal of organic chemistry}, volume = {2020}, journal = {Europan journal of organic chemistry}, number = {11}, publisher = {Wiley}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.202000093}, pages = {1732 -- 1744}, year = {2020}, abstract = {We report on a further development of [1,3]-dioxolo[4.5-f]benzodioxole (DBD) fluorescent dyes by replacement of the four oxygen atoms of the heterocyclic core by sulfur atoms. This variation causes striking changes of the photophysical properties. Whereas absorption and emission significantly shifted to longer wavelength, the fluorescence lifetimes and quantum yields are diminished compared to DBD dyes. The latter effect is presumably caused by an enhanced intersystem crossing to the triplet state due to the sulfur atoms. The very large Stokes shifts of the S-4-DBD dyes ranging from 3000 cm(-1) to 7400 cm(-1) (67 nm to 191 nm) should be especially emphasized. By analogy with DBD dyes a broad variation of absorption and emission wavelength is possible by introducing different electron withdrawing substituents. Moreover, some derivatives for coupling with biomolecules were developed.}, language = {en} } @misc{KruegerKellingLinkeretal.2019, author = {Krueger, Tobias and Kelling, Alexandra and Linker, Torsten and Schilde, Uwe}, title = {Crystal structures of three cyclohexane‑based γ‑spirolactams}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {738}, doi = {10.25932/publishup-43491}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-434911}, pages = {9}, year = {2019}, abstract = {The title compounds, 2-azaspiro[4.5]deca-1-one, C₉H₁₅NO, (1a), cis-8-methyl-2-azaspiro[4.5]deca-1-one, C₁₀H₁₇NO, (1b), and trans-8-methyl-2-azaspiro[4.5]deca-1-one, C₁₀H₁₇NO, (1c), were synthesized from benzoic acids 2 in only 3 steps in high yields. Crystallization from n-hexane afforded single crystals, suitable for X-ray diffraction. Thus, the configurations, conformations, and interesting crystal packing effects have been determined unequivocally. The bicyclic skeleton consists of a lactam ring, attached by a spiro junction to a cyclohexane ring. The lactam ring adopts an envelope conformation and the cyclohexane ring has a chair conformation. The main difference between compound 1b and compound 1c is the position of the carbonyl group on the 2-pyrrolidine ring with respect to the methyl group on the 8-position of the cyclohexane ring, which is cis (1b) or trans (1c). A remarkable feature of all three compounds is the existence of a mirror plane within the molecule. Given that all compounds crystallize in centrosymmetric space groups, the packing always contains interesting enantiomer-like pairs. Finally, the structures are stabilized by intermolecular N-H···O hydrogen bonds.}, language = {en} } @article{KruegerBramborgKellingetal.2021, author = {Kr{\"u}ger, Tobias and Bramborg, Andrea and Kelling, Alexandra and Sperlich, Eric and Linker, Torsten}, title = {Birch Reduction of Arenes as an Easy Entry to γ-Spirolactones}, series = {European journal of organic chemistry}, volume = {2021}, journal = {European journal of organic chemistry}, number = {46}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.202101018}, pages = {6383 -- 6391}, year = {2021}, abstract = {A convenient method for the synthesis of γ-spirolactones in only 2-3 steps is described. Birch reduction of inexpensive and commercially available aromatic carboxylic acids in the presence of ethylene oxide affords hydroxy acids, which undergo direct lactonization during work-up. Suitable precursors are methyl-substituted benzoic acids, naphthoic, and dicarboxylic acids. Subsequent hydrogenation proceeds smoothly with Pd/C as catalyst and saturated γ-spirolactones are isolated in excellent yields and stereoselectivities. Thus, up to 3 new stereogenic centers can be constructed as sole diastereomers from achiral benzoic acids. Furthermore, it is possible to control the degree of saturation with Raney nickel or Wilkinson's catalyst to obtain products with 1 double bond. Overall, more than 30 new γ-spirolactones have been synthesized in analytically pure form.}, language = {en} } @article{KruegerKellingSchildeetal.2016, author = {Kr{\"u}ger, Tobias and Kelling, Alexandra and Schilde, Uwe and Linker, Torsten}, title = {Simple Synthesis of gamma-Spirolactams by Birch Reduction of Benzoic Acids}, series = {European journal of organic chemistry}, journal = {European journal of organic chemistry}, number = {6}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.201601650}, pages = {1074 -- 1077}, year = {2016}, abstract = {A convenient synthesis of gamma-spirolactams in only two steps was developed. Birch reduction of benzoic acids and immediate alkylation with chloroacetonitrile afforded cyclohexadienes in high yields. The products could be isolated by crystallization on a large scale in analytically pure form. Subsequent hydrogenation with platinum(IV) oxide as the catalyst reduced the nitrile functionality and the double bonds in the same step with excellent stereoselectivity. The relative configurations were determined unequivocally by X-ray analyses. Direct cyclization of the intermediary formed amino acids afforded the desired gamma-spirolactams in excellent overall yields. The procedure is characterized by few steps, cheap reagents, and can be performed on a large scale, interesting for industrial processes.}, language = {en} } @article{ZabelWinterKellingetal.2016, author = {Zabel, Andr{\´e} and Winter, Alette and Kelling, Alexandra and Schilde, Uwe and Strauch, Peter}, title = {Tetrabromidocuprates(II)-Synthesis, Structure and EPR}, series = {International journal of molecular sciences}, volume = {17}, journal = {International journal of molecular sciences}, number = {4}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/ijms17040596}, pages = {14}, year = {2016}, abstract = {Metal-containing ionic liquids (ILs) are of interest for a variety of technical applications, e.g., particle synthesis and materials with magnetic or thermochromic properties. In this paper we report the synthesis of, and two structures for, some new tetrabromidocuprates(II) with several "onium" cations in comparison to the results of electron paramagnetic resonance (EPR) spectroscopic analyses. The sterically demanding cations were used to separate the paramagnetic Cu(II) ions for EPR measurements. The EPR hyperfine structure in the spectra of these new compounds is not resolved, due to the line broadening resulting from magnetic exchange between the still-incomplete separated paramagnetic Cu(II) centres. For the majority of compounds, the principal g values (g|| and gK) of the tensors could be determined and information on the structural changes in the [CuBr4]2- anions can be obtained. The complexes have high potential, e.g., as ionic liquids, as precursors for the synthesis of copper bromide particles, as catalytically active or paramagnetic ionic liquids.}, language = {en} } @misc{ZabelWinterKellingetal.2016, author = {Zabel, Andr{\´e} and Winter, Alette and Kelling, Alexandra and Schilde, Uwe and Strauch, Peter}, title = {Tetrabromidocuprates(II)-Synthesis, Structure and EPR}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-91470}, pages = {14}, year = {2016}, abstract = {Metal-containing ionic liquids (ILs) are of interest for a variety of technical applications, e.g., particle synthesis and materials with magnetic or thermochromic properties. In this paper we report the synthesis of, and two structures for, some new tetrabromidocuprates(II) with several "onium" cations in comparison to the results of electron paramagnetic resonance (EPR) spectroscopic analyses. The sterically demanding cations were used to separate the paramagnetic Cu(II) ions for EPR measurements. The EPR hyperfine structure in the spectra of these new compounds is not resolved, due to the line broadening resulting from magnetic exchange between the still-incomplete separated paramagnetic Cu(II) centres. For the majority of compounds, the principal g values (g|| and gK) of the tensors could be determined and information on the structural changes in the [CuBr4]2- anions can be obtained. The complexes have high potential, e.g., as ionic liquids, as precursors for the synthesis of copper bromide particles, as catalytically active or paramagnetic ionic liquids.}, language = {en} } @article{SchildeKellingUmbreenetal.2016, author = {Schilde, Uwe and Kelling, Alexandra and Umbreen, Sumaira and Linker, Torsten}, title = {Crystal structures of three bicyclic carbohydrate derivatives}, series = {Acta crystallographica Section E ; Crystallographic communications}, volume = {72}, journal = {Acta crystallographica Section E ; Crystallographic communications}, number = {12}, publisher = {IUCR}, address = {Chester}, issn = {2056-9890}, doi = {10.1107/S2056989016018727}, pages = {1839 -- 1844}, year = {2016}, abstract = {The title compounds, [(1R,3R,4R,5R,6S)-4,5-bis(acetyloxy)-7-oxo-2-oxabicyclo- [4.2.0]octan-3-yl]methyl acetate, C14H18O8, (I), [(1S,4R,5S,6R)-5-acetyloxy-7- hydroxyimino-2-oxobicyclo[4.2.0]octan-4-yl acetate, C11H15NO6, (II), and [(3aR,5R,6R,7R,7aS)-6,7-bis(acetyloxy)-2-oxooctahydropyrano[3,2-b]pyrrol-5- yl]methyl acetate, C14H19NO8, (III), are stable bicyclic carbohydrate derivatives. They can easily be synthesized in a few steps from commercially available glycals. As a result of the ring strain from the four-membered rings in (I) and (II), the conformations of the carbohydrates deviate strongly from the ideal chair form. Compound (II) occurs in the boat form. In the five-membered lactam (III), on the other hand, the carbohydrate adopts an almost ideal chair conformation. As a result of the distortion of the sugar rings, the configurations of the three bicyclic carbohydrate derivatives could not be determined from their NMR coupling constants. From our three crystal structure determinations, we were able to establish for the first time the absolute configurations of all new stereocenters of the carbohydrate rings.}, language = {en} } @misc{SchildeKellingUmbreenetal.2016, author = {Schilde, Uwe and Kelling, Alexandra and Umbreen, Sumaira and Linker, Torsten}, title = {Crystal structures of three bicyclic carbohydrate derivatives}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-100833}, pages = {6}, year = {2016}, abstract = {The title compounds, [(1R,3R,4R,5R,6S)-4,5-bis­(acet­yloxy)-7-oxo-2-oxabi­cyclo[4.2.0]octan-3-yl]methyl acetate, C14H18O8, (I), [(1S,4R,5S,6R)-5-acet­yloxy-7-hy­droxy­imino-2-oxobi­cyclo­[4.2.0]octan-4-yl acetate, C11H15NO6, (II), and [(3aR,5R,6R,7R,7aS)-6,7-bis­(acet­yloxy)-2-oxo­octa­hydro­pyrano[3,2-b]pyrrol-5-yl]methyl acetate, C14H19NO8, (III), are stable bicyclic carbohydrate derivatives. They can easily be synthesized in a few steps from commercially available glycals. As a result of the ring strain from the four-membered rings in (I) and (II), the conformations of the carbohydrates deviate strongly from the ideal chair form. Compound (II) occurs in the boat form. In the five-membered lactam (III), on the other hand, the carbohydrate adopts an almost ideal chair conformation. As a result of the distortion of the sugar rings, the configurations of the three bicyclic carbohydrate derivatives could not be determined from their NMR coupling constants. From our three crystal structure determinations, we were able to establish for the first time the absolute configurations of all new stereocenters of the carbohydrate rings.}, language = {en} } @article{SieboldKellingSchildeetal.2005, author = {Siebold, M. and Kelling, Alexandra and Schilde, Uwe and Strauch, Peter}, title = {Heterobimetallic 3d-4-complexes with bis(1;2-dithiooxalato)nickelate(II) as planar bridging block}, issn = {0932-0776}, year = {2005}, abstract = {Planar bis(1,2-dithiooxalato)nickelates(II) react in aqueous solutions of lanthanide ions to form pentanuclear, heterobimetallic complexes of the general composition [{Ln(H2O)(n)}(2)- {Ni(dto)(2)}(3)] (.) xH(2)O (Ln = Y3+, La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Yb3+, Lu3+; n = 4 or 5; x = 9-12). With [{Nd(H2O)(5)}(2){Ni(S2C2O2)(2)}(3)] (.) xH(2)O (x = 10-12) (1) and [{Er(H2O)(4)}(2){Ni(S2C2O2)(2)}(3)] (.) xH(2)O (x = 9- 10) (2) we were able to isolate two complexes of this series as single crystals, which were characterized by X-ray structure analysis. Depending on the individual ionic radii of the lanthanide ions, the compounds crystallize in two different crystal systems with the following unit cell parameters: 1, monoclinic in P2(1)/c with a = 11.3987(13), b = 11.4878(8), c = 20.823(2)angstrom , beta = 98.907(9)degrees and Z = 2; 2, triclinic in P (1) over bar with a = 10.5091(6), b = 11.0604(6), c = 11.2823(6) angstrom, alpha = 107.899(4)degrees, beta = 91.436(4)degrees, gamma = 112.918(4)degrees and Z = 1. The channels and cavities appearing in the packing of the molecules are occupied by uncoordinated water molecules. High magnetic moments up to 14.65 BM./f.u. have been observed at room temperature due to the combined moments of the individual lanthanide ions}, language = {en} }