Werner Riemer

(Diethyl muconate)(1,4-diaza-1,3-diene)carbonyliron complexes: syntheses, spectra, and structure

Three examples of a new type of mixed (1,3-diene)(1,4-diaza-1,3-diene)carbonyliron complexes have been prepared. The diene ligand is diethyl muconate, trans , trans -H 5 C 2 OOCCHCHCHCHCOOC 2 H 5 , and the 1,4-diaza-1,3-diene (DAD) ligands are 2,2′-bipyridyl (BIPY) and the Schiff bases 2-benzoylpyridineanil (BPA) and 2-benzoylpyridine- p -methoxyanil (BPpMA). The complexes were made by thermal substitution of one diene ligand of bis(muconate)carbonyliron by the respective DAD ligands, and photochemically from (muconate)tricarbonyliron and DAD by substitution of two CO ligands. The structure of (muconate)(BIPY)Fe(CO) (I) was established by an X-ray analysis (cell data: a = 9.648(2) », b = 11.422(2) », c = 19.080(2) », β = 100.77(2)°; space group P2 1 / n , R = 0.048). The complex approximates to a square pyramid with one of the BIPY nitrogen atoms occupying the apical position. IR, UV, and mass spectra are reported. The 1 H and 13 C NMR spectra reveal the unsymmetrical structure. The complexes II (with BPA) and III (with BPpMA) are mixtures of isomers. The spectral data indicate structures analogous to I.

Zur Kenntnis organischerLewis-Säuren, 36.Cis—trans-Gleichgewichte und Konformationen von 2,(x)-Dialkyl-1-dicyanomethylencyclohexanen. Wahlweise einfache Darstellung dercis- odertrans-Formen

Knoevenagel condensation of malononitrile withcis- andtrans-2,5-dimethylcyclohexanone (1c and1t, respectively) leads to2c and2t, respectively, and withtrans-1-decalone to4t. The equilibria2c⇌2t and4c⇌4t have been determined as well as, by means of 270-MHz-1H-NMR, the conformations of these four compounds. The dicyanomethylene group is found to induce axial positions of neighbouring alkyl residues on the cyclohexane ring (or when this is impossible, as in the case of4t, the twist form of the cyclohexane ring). This results in a strong predominance of thecis isomers in the equilibria2c⇌2t and4c⇌4t whereas thetrans isomers strongly predominate in the equilibria among the starting ketones. This situation allows the optional preparation of2c or2t, and of4c or4t, from the more stable starting ketone (or ketone mixture). The free conformational energy of the distorted twist form of4t amounts to 17 kJ/mol.

Die ringgrösse des galacturonsäurebausteins im antibiotikum moenomycin a

Zusammenfassung Ring size of the galacturonic acid part of the moenomycin A degradation products 1, 2, and 3 has been determined

Zur struktur des antibiotikums moenomycin A

Zusammenfassung Degradation products 4 and 5 of the antibiotic moenomycin A have been identified. Partial structures 3 and 6 of moenomycin A can now be formulated, connection of these units will probably provide the complete structure of the antibiotic.

Die Photoenolisierung, Autoxidation und Dimerisation von 2-Isobutyliden-1,3-indandion

AbstractThe title compound,1, slowly decomposes in solution by autodixation, especially in daylight. The chemism of this photoinduced autoxidation has been investigated.Upon irradiation1 passes to the brick red isolable dienol2. The quantum yield is 0.3 at 313 nm in methanol. In solution an equilibrium is set up within several minutes between2 and the colorless deconjugated3. Unpolar or moderately polar solvents shift the equilibrium completely to3, whereas in highly polar solvents2 and3 coexist. In the dark the equilibrium1⇄2 (ca. 50∶1 in methanol) is established very slowly.3 upon irradiation reacts further to dimer8. 2 instantaneously reacts with oxygen. With high oxygen concentrations, hydroperoxide9 is formed, with lower ones dehydrodimer10, inter alia.9 and10 may further form12, 14, and15. These reactions, together with ESR spectroscopy, point to a central role of the free radical13 both in the autoxidation and in the reaction10→14.Basic catalysis sets up an equilibrium between1 and its dimer,17. The photoreaction1→2 has been investigated by sensitizing and quenching experiments.