TY - JOUR A1 - Fudickar, Werner A1 - Metz, Melanie A1 - Mai-Linde, Yasemin A1 - Krüger, Tobias A1 - Kelling, Alexandra A1 - Sperlich, Eric A1 - Linker, Torsten T1 - Influence of functional groups on the ene reaction of singlet oxygen with 1,4-cyclohexadienes JF - Photochemistry and photobiology : the official journal of the American Society for Photobiology N2 - 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. Y1 - 2021 U6 - https://doi.org/10.1111/php.13422 SN - 0031-8655 SN - 1751-1097 VL - 97 IS - 6 SP - 1289 EP - 1297 PB - Wiley CY - Malden, Mass. ER - TY - JOUR A1 - Krüger, Tobias A1 - Bramborg, Andrea A1 - Kelling, Alexandra A1 - Sperlich, Eric A1 - Linker, Torsten T1 - Birch Reduction of Arenes as an Easy Entry to γ-Spirolactones JF - European journal of organic chemistry N2 - 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. KW - Arenes KW - Birch reduction KW - Hydrogenation KW - Lactones KW - Synthetic methods Y1 - 2021 U6 - https://doi.org/10.1002/ejoc.202101018 SN - 1434-193X SN - 1099-0690 VL - 2021 IS - 46 SP - 6383 EP - 6391 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Kwesiga, George A1 - Sperlich, Eric A1 - Schmidt, Bernd T1 - Scope and applications of 2,3-oxidative aryl rearrangements for the synthesis of isoflavone natural products JF - The journal of organic chemistry N2 - The reaction of flavanones with hypervalent iodine reagents was investigated with a view to the synthesis of naturally occurring isoflavones. In contrast to several previous reports in the literature, we did not observe the formation of any benzofurans via a ring contraction pathway, but could isolate only isoflavones, resulting from an oxidative 2,3-aryl rearrangement, and flavones, resulting from an oxidation of the flavanones. Although the 2,3-oxidative rearrangement allows a synthetically useful approach toward some isoflavone natural products due to the convenient accessibility of the required starting materials, the overall synthetic utility and generality of the reaction appear to be more limited than previous literature reports suggest. Y1 - 2021 U6 - https://doi.org/10.1021/acs.joc.1c01375 SN - 0022-3263 SN - 1520-6904 VL - 86 IS - 15 SP - 10699 EP - 10712 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Sperlich, Eric A1 - Kelling, Alexandra A1 - Kwesiga, George A1 - Schmidt, Bernd T1 - Intermolecular interactions in the solid-state structures of isoflavones BT - the relationship between supramolecular structure, torsion angle, and macroscopic properties JF - CrystEngComm / The Royal Society of Chemistry N2 - The molecular structures of three closely related isoflavones have been determined by single crystal X-ray diffraction and have been analysed by geometry matching with the CSD, Hirshfeld surface analysis and analysis of stacking interactions with the Aromatic Analyser program (CSD). The formation of the supramolecular structure by non-covalent interactions was studied and substantial differences in the macroscopic properties e.g., the solubility, were correlated with hydrogen bonding and pi-stacking interactions. Moreover, a correlation between the supramolecular structure, the torsion angle (between benzopyran group and aryl group), and macroscopic properties was determined in the three compounds. Y1 - 2022 U6 - https://doi.org/10.1039/d2ce00169a SN - 1466-8033 VL - 24 IS - 26 SP - 4731 EP - 4739 PB - Royal Society of Chemistry CY - London ER - TY - JOUR A1 - Wessig, Pablo A1 - Badetko, Dominik A1 - Czarnecki, Maciej A1 - Wichterich, Lukas A1 - Schmidt, Peter A1 - Brudy, Cosima A1 - Sperlich, Eric A1 - Kelling, Alexandra T1 - Studies toward the total synthesis of arylnaphthalene lignans via a Photo-Dehydro-Diels-Alder (PDDA) reaction JF - The journal of organic chemistry N2 - An efficient method for the preparation of arylnaphthalene lignans (ANLs) was developed, which is based on thePhoto-Dehydro-DIELS-ALDER(PDDA) reaction. While intermolecular PDDA reactions turned out to be inefficient, theintramolecular variant using suberic acid as tether linking two aryl propiolic esters smoothly provided naphthalenophanes. Theirradiations were performed with a previously developed annular continuous-flow reactor and UVB lamps. In this way, the naturalproducts Alashinol D, Taiwanin C, and an unnamed ANL could be prepared. Y1 - 2022 U6 - https://doi.org/10.1021/acs.joc.2c00195 SN - 0022-3263 SN - 1520-6904 VL - 87 IS - 9 SP - 5904 EP - 5915 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Krause, Andreas A1 - Sperlich, Eric A1 - Schmidt, Bernd T1 - Matsuda-Heck arylation of itaconates BT - a versatile approach to heterocycles from a renewable resource JF - Organic & biomolecular chemistry : an international journal of synthetic, physical and biomolecular organic chemistry N2 - Itaconic acid esters and hemiesters undergo Pd-catalyzed coupling reactions with arene diazonium salts in high to excellent yields. The coupling products of ortho-nitro arene diazonium salts can be converted in one or two steps to benzazepine-2-ones. Y1 - 2021 U6 - https://doi.org/10.1039/d1ob00392e SN - 1477-0520 SN - 1477-0539 VL - 19 IS - 19 SP - 4292 EP - 4302 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Sperlich, Eric A1 - Köckerling, Martin T1 - [Nb6Cl12(CH3OH)4(OCH3)2] ⋅ DABCO ⋅ 1.66 CH2Cl2 BT - cluster units wrapped in a network of hydrogen bonds JF - Zeitschrift für anorganische und allgemeine Chemie : ZAAC = Journal of inorganic and general chemistry N2 - An easy-to-do synthesis for the hexanuclear niobium cluster compound [Nb6Cl12(CH3OH)(4)(OCH3)(2)] . DABCO . 1.66 CH2Cl2 has been developed. An one-pot reaction between the cluster precursor [Nb6Cl14(H2O)(4)] . 4H(2)O and methanol with the addition of DABCO leads to the crystallization of the title compound in high yield within a few minutes. The single-crystal X-ray structure of this cluster compound has been determined. Very strong, nearly symmetric intercluster hydrogen bonds Nb-6-MeO...H...OMe-Nb-6 are present between the cluster units. A bridging co-crystalline DABCO molecule is also involved in a three-dimensional hydrogen-bonding network. KW - Niobium KW - Cluster KW - Hydrogen Bonds KW - Synthesis KW - Structure Determination Y1 - 2021 U6 - https://doi.org/10.1002/zaac.202100138 SN - 0044-2313 SN - 1521-3749 VL - 647 IS - 18 SP - 1759 EP - 1763 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Schwarze, Thomas A1 - Sperlich, Eric A1 - Müller, Thomas A1 - Kelling, Alexandra A1 - Holdt, Hans-Jürgen T1 - Synthesis efforts of acyclic bis(monoalkylamino)maleonitriles and macrocyclic bis(dialkylamino)maleonitriles as fluorescent probes for cations and a new colorimetric copper(II) chemodosimeter JF - Helvetica chimica acta N2 - In this article, we report on the synthesis of acyclic bis(monoalkylamino)maleonitriles and on the intended synthesis of macrocyclic bis(dialkylamino)maleonitriles to get fluorescent probes for cations. During our efforts to synthesize macrocyclic bis(dialkylamino)maleonitriles, we were only able to isolate macrocyclic bis(dialkylamino)-fumaronitriles. The synthesis of macrocyclic bis(dialkylamino)maleonitriles is challenging, due to the fact that bis-(dialkylamino)fumaronitriles are thermodynamically more stable than the corresponding bis(dialkylamino)-maleonitriles. Further, it turned out that the acyclic bis(monoalkylamino)maleonitriles and macrocyclic bis-(dialkylamino)fumaronitriles are no suitable tools to detect cations by a strong fluorescence enhancement. Further, only the bis(monoalkylamino)maleonitriles, which are bearing a 2-pyridyl unit as an additional complexing unit, are able to selectively recognize copper(II) by a color change from yellow to red. KW - copper KW - fumaronitrile KW - ligands KW - macrocycles KW - maleonitrile Y1 - 2021 U6 - https://doi.org/10.1002/hlca.202100028 SN - 1522-2675 VL - 104 IS - 6 SP - e2100028 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Schwarze, Thomas A1 - Kelling, Alexandra A1 - Sperlich, Eric A1 - Holdt, Hans-Jürgen T1 - Influence of regioisomerism in 9-anthracenyl-substituted dithiodicyanoethene derivatives on photoinduced electron transfer controlled by intramolecular charge transfer JF - ChemPhotoChem N2 - In this paper, we report on the fluorescence behaviour of three regioisomers which consist of two 9-anthracenyl fluorophores and of differently substituted dithiodicyanoethene moieties. These isomeric fluorescent probes show different quantum yields (phi(f)). In these probes, an oxidative photoinduced electron transfer (PET) from the excited 9-anthracenyl fluorophore to the dithiodicyanoethene unit quenches the fluorescence. This quenching process is accelerated by an intramolecular charge transfer (ICT) of the push-pull pi-electron system of the dithiodicyanoethene group. The acceleration of the PET depends on the strength of the ICT unit. The higher the dipole moment of the ICT unit, the stronger the observed fluorescence quenching. To the best of our knowledge, this is the first report of a regioisomeric influence on an oxidative PET by an ICT. KW - anthracene KW - charge transfer KW - electron transfer KW - fluorescence KW - isomerism Y1 - 2021 U6 - https://doi.org/10.1002/cptc.202100070 SN - 2367-0932 VL - 5 IS - 10 SP - 911 EP - 914 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Sperlich, Eric A1 - Köckerling, Martin T1 - [Nb6Cl14(pyrazine)(4)], a versatile precursor for ligand-supported hexanuclear niobium cluster compounds: synthesis, characterization, follow-up reactions, and intermolecular interactions JF - Inorganic chemistry N2 - The compound [Nb6Cl14(pyrazine)(4)]center dot 2CH(2)Cl(2) (1) was investigated for its suitability as a starting compound for new ligand-supported hexanuclear niobium cluster compounds. The synthesis, stability to air and increased temperature, solubility and usability for subsequent reactions of 1, and purification and separation of the reaction products are discussed. The compounds with cluster units [Nb6Cl14L4], where L = iso-quinoline N-oxides (2), 1,1-dimethylethylenediamines (3), or thiazoles (4), and [Nb6Cl14(PEt3)(3.76)(Et3PO)(0.24)]-[Nb6Cl14(MeCN)(4)]center dot 4MeCN (5) are presented as follow-up products. The crystal structures of compounds 1-5 are analyzed, and the structures are discussed with respect to their intraand intermolecular bonding situations and crystal packing. In addition to hydrogen bonds and pi-pi interactions, the appearance of chalcogen and halogen bonds and lone pair-pi interactions between Nb-6 cluster units was observed for the first time. KW - Cluster chemistry KW - crystals KW - ligands KW - molecules KW - transition metals Y1 - 2022 U6 - https://doi.org/10.1021/acs.inorgchem.1c03109 SN - 0020-1669 SN - 1520-510X VL - 61 IS - 5 SP - 2409 EP - 2420 PB - American Chemical Society CY - Washington ER -