Capto-dative Substituent Effects in Syntheses with Radicals and Radicophiles [New synthetic methods (32)]

The 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto-dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd-Substitution has synthetically useful applications: cd-substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross-conjugated cd-substituents are “radicophilic” and permit twofold carbon radical addition. cd-Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd-substituted molecules appear to involve radicals.     

Beiträge zur Chemie der Pyrrolpigmente, 20. Mitt.: Untersuchungen über das Deprotonierungsgleichgewicht und die Bildung von Metallkomplexen von Gallenpigment-Partialstrukturen

By spectrophotometric measurements in the systemDMSO/H₂O/Me ₄NOH pK _a-values for several model compounds representing bile pigment partial structures were established. The acidic protons of pyrrole and lactame type nitrogen atoms are removed by bases governed by the electronic properties of the substituents on these ring systems. The pK _a-values for both types lie in the same region. In the pyrromethenones the lower one corresponds to the lactame type NH as was deduced by comparison with specifically methylated derivatives.The complexation of these ligands is determined by the possibility of removing an acidic proton and achieving a chelate structure by means of an adjacent pyrrolinone type nitrogen atom. Complexes are favoured in the series pyrromethenes > lactim ethers > pyrromethenones. With the latter there are two possibilities: one observed with BF₂-chelation where the lactime form becomes stabilized, the other one with zink where both acidic centers are involved in the bonding.

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19. Mitt.:H. Falk, A. Leodolter undG. Schade, Mh. Chem.109, 183 (1978).     

Polysulfonylamine. CLX [1] Kristallstrukturen von Metall‐di(methansulfonyl)amiden. 10 [2] Die dreidimensionalen Koordinationspolymere M[(CH3SO2)2N] mit M = Kalium,Rubidium, Caesium (isotype Strukturen für M = K,Rb)

Polysulfonylamines. CLX. Crystal Structures of Metal Di(methanesulfonyl)amides. 10. The Three‐Dimensional Coordination Polymers M[(CH₃SO₂)₂N], where M is Potassium, Rubidium, Cesium (Isotypic Structures for M = K, Rb) Low‐temperature X‐ray crystal structures are reported for KA (monoclinic, space group P2₁/c, Z′ = 1), RbA (isotypic and isostructural with KA), and CsA (monoclinic, P2₁/n, Z′ = 1), where A^— denotes the anion obtained by deprotonation of the strong nitrogen acid (MeSO₂)₂NH. In KA and RbA, the anion is distorted into a rare C₁ conformation, whereas the standard C₂ conformation is retained in the cesium complex. The structures consist of three‐dimensional coordination networks, in which each cation adopts an irregular (O₆N)‐heptacoordination by forming close contacts to one (O, N)‐chelating, one (O, O)‐chelating and three κ¹O‐bonding ligands; however, the coordination number for Cs⁺ is effectively increased to 8 by a very short Cs···Cs contact distance of 422.5 pm. The crystal packings of the isotypic compounds KA and RbA display lamellar layer substructures that involve six independent ligand‐metal bonds and comprise an internal cation lamella and peripheral regions built up from anion monolayers; the 3D framework is completed by one independent M—O bond cross‐linking the layer substructures. In contrast, CsA features anion monolayers that intercalate planar zigzag chains of cations (Cs···Cs alternatingly 422.5 and 487.5 pm, Cs···Cs···Cs 135.7°), whereby each chain is surrounded and coordinated by four anion stacks and each anion stack connects two cation chains. All structures exhibit close C—H···A interanion contacts consistent with weak hydrogen bonding.     

Chemie der Pleuromutiline,IX. Konfigurationsumkehr der Methylgruppe am Kohlenstoff 6 im tricyclischen Gerüst des Diterpens Pleuromutilin

The contact of pleuromutilin derivatives with the protein moiety of cytochrome P-450 as well as its orientation towards the heme iron is mainly dependent on the steric environment of the hydrindanone-part of the tricyclus. The apparent affinity between substrate and enzyme, which is correlated with the rate of metabolism can be reduced by inversion of configuration at carbon 6. This inversion is achieved by equilibrating the diastereomeric ketones12 and13 followed by a selective reduction of the keto group at position 7. The 6-methylgroup of14 was assigned α-configuration on the basis of spectroscopic data in comparison to those of the naturally configurated compound14a.     

Zur Chemie der Pyrrolpigmente, 54. Mitt.: Phytochrommodellstudien: Ein 2,3-Dihydrobilatrien-abc-3-Cholesterylderivat

The diastereomeric 2,3-Dihydrobilatrienes-abc derivatives (4Z, 9Z, 15Z)-7 and (4Z, 9Z, 15E)-7 bearing a cholesterylacetate moiety in position 3 of the chromophore are prepared. The reaction sequence contains an isomerisation step providing quantitative enantioselective formation of the chiral center in position 3. Configurations and conformations of the diastereomers are elucidated using¹H- and¹³C-NMR spectra, NOE-difference spectra, 2D-NMR experiments (NOESY) and arguments from UV-VIS and CD data. It is concluded that the hydrophobic interactions between chromophore and cholesteryl-fragment yield a compact conformation where the two substructures are in close contact with each other. On the other hand these interactions seem to be too weak to induce significant changes in the chemistry, absorption spectra and conformational characterics of the bile pigment chromophore. Therefore hydrophobic interactions between chromophor and apolar amino acid residues of the protein in phytochrome should be of minor relevance for determining spectroscopic shifts.

     

Stereoselective formation of ansa-metallocenes in reactions of radical-anionic salts of acenaphthylene with lanthanide and calcium halides

ansa-Metallocenes (⁵:⁵-C₂₄H₁₆)M(THF)₂ (M = Sm (1), Yb (2), Ca (3)) and (⁵:⁵-C₂₄H₁₆)MI(THF) (M = Dy (8), Er (9), Tm (10), Lu (11)) were prepared in 50—90% yields by the in situ reactions of two equivalents of potassium acenaphthylenide K⁺C₁₂H₈ ^– with MI₂ or MI₃, respectively. Complexes 2 and 3 were also obtained by direct reduction of acenaphthylene with ytterbium and calcium naphthalenides, respectively. An ESR signal of the acenaphthylene radical anion, which was observed upon dissolution of compound 2 in THF, indicates that the [C₂₄H₁₆]^2– ansa-ligand dissociated into two [C₁₂H₈]^·– radical anions. Hydrolysis of complex 2 in benzene afforded 1,1",3,3"-tetrahydro-3,3"-biacenaphthylene (4) and 3,3",4,4"-tetrahydro-3,3"-biacenaphthylene (5). The reaction of complex 2 with ZrCl₄ and the reaction of compound 3 with Me₃SiCl proceeded with the cleavage of the C—C bond between two acenaphthylene fragments of the [C₂₄H₁₆]^2– ansa-ligand to produce (²-C₁₂H₈)ZrCl₂(THF)₃ (6) and bis(trimethylsilyl)acenaphthene (Me₃Si)₂C₁₂H₈ (7), respectively. Compounds 1—3, 6, 7, and 11 were characterized by ¹H and ¹³C NMR spectroscopy. The temperature dependence of the ¹H NMR spectrum of compound 11 in tetrahydrofuran is indicative of the dynamic exchange of the solvent molecules in the coordination sphere of the Lu atom. After cooling of the solution to 210 K, the dynamic process was terminated as evidenced by the nonequivalence of the ¹H signals of two acenaphthylene fragments. According to the X-ray diffraction data for complex 11, dimerization of two acenaphthylene radical anions at the Lu atom gave rise to the rac-ansa-metallocene structure. In compound 11, the Lu atom is ⁵-coordinated by two five-membered rings of the acenaphthylene ligands and also by the I atom and the THF molecule. The coordination environment about the Lu atom is a distorted tetrahedron. The average distance between the lutetium atom and the carbon atoms of the five-membered rings is 2.623 .     

On the synthesis of hypericin by oxidative trimethylemodin anthrone and emodin anthrone dimerization: Isohypericin

Summary The base catalyzed oxidative dimerization of emodin anthrone exclusively yields hypericin. However, on oxidative dimerization of trimethylemodinanthrone a mixture of hexamethylhypericin and hexamethylisohypericin was obtained. Chromatographic separation of the hexabenzoyl derivatives was achieved, and by saponification about equal amounts of hypericin and isohypericrin were produced. Isohypericin could be characterized for the first time by its spectroscopic data and its protonation and deprotonationpK _a andpK _a ^* values.

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Zur Synthese von Hypericin durch oxidative Dimerisierung von Trimethylemodinanthron und Emodinanthron: Isohypericin

Zusammenfassung Die basenkatalysierte oxidative Dimerisierung von Emodinanthron liefert ausschließlich Hypericin. Oxidative Dimerisierung von Trimethylemodinanthron ergibt jedoch ein Gemisch von Hexamethylhypericin und Hexamethylisohypericin. Die Hexabenzoylderivate wurden chromatographisch getrennt, und Hypericin und Isohypericin konnten aus diesen Derivaten durch Verseifung freigesetzt werden. Isohypercin konnte erstmals durch seine spektroskopischen Daten und seine Protonierungs- und Deprotonierungs-pK _aundpK _a ^* -Werte charakterisiert werden.

     

2-Amino-1-cyan-glutaconsäureamid-1-methylester,ein Dimeres des Cyanessigesters und Cyanacetamid

Synthesis of methyl 3-amino-4-carbomyl-2-cyano-2-butenoate is described and2 a classified as a dimer of methyl cyanoacetate and cyanoacetamide. By ammonolysis of the dimer of methyl cyanoacetate with dimethylamine and anilines, resp. the dimethylamide and anilides, resp. (2 b and3 a–j) are obtained. Condensation with salicylaldehyde to the pyrone derivative4 proves the structure of2 a, ring closure reactions in basic or acidic medium yield the pyridones6 a and7 a,b, coupling with diazonium salts the pyridazines8 a–d. The amides2 and the anilides3 show hindered rotation of the enamino- and the amide-group by hydrogen bonds between the nitrogen functions and the ester carbonyl (Z-form). The G values are reported.

     

Über Triäthanolaminkomplexe

Zusammenfassung Kristallstrukturelle Untersuchungen an Zinkchlorid-Triäthanolaminverbindungen haben innermolekulare Triäthanolaminkomplexe mit koordinativer Metall-Stickstoffbindung ergeben. Dieses Resultat kann bei bestimmten Verbindungen verallgemeinert werden.

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Triethanolamine complexes

Crystal structures of ZnCl₂-triethanolamine compounds have been determined. The triethanolamine complexes contain atrans-anular donor-acceptor bond between metal and nitrogen. It is possible to apply this result to different triethanolamine compounds.

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Mit 4 Abbildungen

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Nach einem Vortrag auf der 11. Diskussionstagung der Sektion für Kristallkunde der Deutschen Mineralogischen Gesellschaft in Saarbrücken 1970.     

Determination of geosmin and 2-methylisoborneol in water using solid-phase microextraction and gas chromatography-chemical ionisation/electron impact ionisation-ion-trap mass spectrometry

A method for the determination of geosmin and 2-methylisoborneol (MIB) in water by solid-phase microextraction (SPME) is presented. Various SPME fibre chemistries have been compared for their efficiency in extracting MIB from water. Extraction conditions including the extraction time and temperature have been optimised. A 30 ml water sample is extracted for 20 min at 60 degrees C using a divinylbenzene fibre, and the extract analysed by gas chromatography with ion-trap mass spectrometry detection. d5-Geosmin and d3-MIB are added as internal standards to compensate for any variability in the SPME process which is not carried out to equilibrium. Chemical ionisation, using acetonitrile as the reagent gas, was found to give superior sensitivity to electron impact ionisation (EI) for the detection of MIB. EI was used as the ionisation mode for detection of geosmin. The method shows good linearity over the concentration range 5-40 ng l-1 and gives detection limits of 1 ng l-1 for both geosmin and MIB. Recovery (93-110%) and precision (3-12%) over this concentration range, for both raw and treated drinking waters, are comparable to currently employed methods such as closed-loop stripping analysis (CLSA). The method offers the advantage of being simple to use, with much shorter analysis times in comparison to CLSA.