@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{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{KwesigaSperlichSchmidt2021, author = {Kwesiga, George and Sperlich, Eric and Schmidt, Bernd}, title = {Scope and applications of 2,3-oxidative aryl rearrangements for the synthesis of isoflavone natural products}, series = {The journal of organic chemistry}, volume = {86}, journal = {The journal of organic chemistry}, number = {15}, publisher = {American Chemical Society}, address = {Washington}, issn = {0022-3263}, doi = {10.1021/acs.joc.1c01375}, pages = {10699 -- 10712}, year = {2021}, abstract = {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.}, language = {en} } @article{SperlichKellingKwesigaetal.2022, author = {Sperlich, Eric and Kelling, Alexandra and Kwesiga, George and Schmidt, Bernd}, title = {Intermolecular interactions in the solid-state structures of isoflavones}, series = {CrystEngComm / The Royal Society of Chemistry}, volume = {24}, journal = {CrystEngComm / The Royal Society of Chemistry}, number = {26}, publisher = {Royal Society of Chemistry}, address = {London}, issn = {1466-8033}, doi = {10.1039/d2ce00169a}, pages = {4731 -- 4739}, year = {2022}, abstract = {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.}, language = {en} } @article{WessigBadetkoCzarneckietal.2022, author = {Wessig, Pablo and Badetko, Dominik and Czarnecki, Maciej and Wichterich, Lukas and Schmidt, Peter and Brudy, Cosima and Sperlich, Eric and Kelling, Alexandra}, title = {Studies toward the total synthesis of arylnaphthalene lignans via a Photo-Dehydro-Diels-Alder (PDDA) reaction}, series = {The journal of organic chemistry}, volume = {87}, journal = {The journal of organic chemistry}, number = {9}, publisher = {American Chemical Society}, address = {Washington}, issn = {0022-3263}, doi = {10.1021/acs.joc.2c00195}, pages = {5904 -- 5915}, year = {2022}, abstract = {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.}, language = {en} } @article{KrauseSperlichSchmidt2021, author = {Krause, Andreas and Sperlich, Eric and Schmidt, Bernd}, title = {Matsuda-Heck arylation of itaconates}, series = {Organic \& biomolecular chemistry : an international journal of synthetic, physical and biomolecular organic chemistry}, volume = {19}, journal = {Organic \& biomolecular chemistry : an international journal of synthetic, physical and biomolecular organic chemistry}, number = {19}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1477-0520}, doi = {10.1039/d1ob00392e}, pages = {4292 -- 4302}, year = {2021}, abstract = {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.}, language = {en} } @article{SperlichKoeckerling2021, author = {Sperlich, Eric and K{\"o}ckerling, Martin}, title = {[Nb6Cl12(CH3OH)4(OCH3)2] ⋅ DABCO ⋅ 1.66 CH2Cl2}, series = {Zeitschrift f{\"u}r anorganische und allgemeine Chemie : ZAAC = Journal of inorganic and general chemistry}, volume = {647}, journal = {Zeitschrift f{\"u}r anorganische und allgemeine Chemie : ZAAC = Journal of inorganic and general chemistry}, number = {18}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0044-2313}, doi = {10.1002/zaac.202100138}, pages = {1759 -- 1763}, year = {2021}, abstract = {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.}, language = {en} } @article{SchwarzeSperlichMuelleretal.2021, author = {Schwarze, Thomas and Sperlich, Eric and M{\"u}ller, Thomas and Kelling, Alexandra and Holdt, Hans-J{\"u}rgen}, title = {Synthesis efforts of acyclic bis(monoalkylamino)maleonitriles and macrocyclic bis(dialkylamino)maleonitriles as fluorescent probes for cations and a new colorimetric copper(II) chemodosimeter}, series = {Helvetica chimica acta}, volume = {104}, journal = {Helvetica chimica acta}, number = {6}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1522-2675}, doi = {10.1002/hlca.202100028}, pages = {e2100028}, year = {2021}, abstract = {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.}, language = {en} } @article{SchwarzeKellingSperlichetal.2021, author = {Schwarze, Thomas and Kelling, Alexandra and Sperlich, Eric and Holdt, Hans-J{\"u}rgen}, title = {Influence of regioisomerism in 9-anthracenyl-substituted dithiodicyanoethene derivatives on photoinduced electron transfer controlled by intramolecular charge transfer}, series = {ChemPhotoChem}, volume = {5}, journal = {ChemPhotoChem}, number = {10}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {2367-0932}, doi = {10.1002/cptc.202100070}, pages = {911 -- 914}, year = {2021}, abstract = {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.}, language = {en} } @article{SperlichKoeckerling2022, author = {Sperlich, Eric and K{\"o}ckerling, Martin}, title = {[Nb6Cl14(pyrazine)(4)], a versatile precursor for ligand-supported hexanuclear niobium cluster compounds: synthesis, characterization, follow-up reactions, and intermolecular interactions}, series = {Inorganic chemistry}, volume = {61}, journal = {Inorganic chemistry}, number = {5}, publisher = {American Chemical Society}, address = {Washington}, issn = {0020-1669}, doi = {10.1021/acs.inorgchem.1c03109}, pages = {2409 -- 2420}, year = {2022}, abstract = {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.}, language = {en} }