Über die Strukturaufklärung von (Hydroxy-oxo-cyclopentenyl)alkansäuren,den Aldolkondensationsprodukten von Dioxoencarbonsäuren aus Rinderleber

Structure Elucidation of (Hydroxy-oxo-cyclopentenyl)alkanoic Acids, the Aldol-Condensation Products of Dioxoene Acids from Cattle Liver During homogenization of cattle liver the highly instable dioxoene acids 13a , 13b , and 13c are formed. These acids cyclize in alkaline solution to yield pairs of stable (hydroxy-oxo-cyclopentenyl)alkanoic acids, which were isolated as methyl esters 4a / 5a , 4b / 5b , and 4c / 5c . The structures of these compounds were deduced from an enriched 3-mg mixture sample by microchemical reactions combined with a GC/MS analysis of the reaction products. Compound 13a was obtained as methyl ester by oxidation of the methyl ester of the corresponding F-acid with NaOCl. It was not possible to isolate 13a in pure form due to its high sensitivity. Instead of the methyl ester of 13a , 4a and 5a were isolated, of which the structures were established.     

Electrochemistry of capillary systems with narrow pores. IV. Dialysis potentials

The dialysis potentials of different collodion membranes with graded pore sizes and electrochemical activities have been measured in dilute aqueous KCl solutions as functions of concentration. It is possible to predict the value of the diffusion potential within a few millivolts on the basis of electrical conductivity data obtained with the same membranes. In general, the measured values are lower than those calculated. It is assumed that this difference is caused by the membranes having a distribution of pore sizes.     

Asymmetric synthesis of 2,3-dihydrofurans and of unsaturated bicyclic tetrahydrofurans through alpha-elimination and migratory cyclization of silyloxy alkenyl aminosulfoxonium salts. Generation and intramolecular O,Si-bond insertion of chiral disubstituted beta-silyloxy alkylidene carbenes

Treatment of the bis(allylsulfoximine)titanium complexes derived from the beta-methyl-substituted acyclic allylic sulfoximines 13a and 13b with aldehydes gave with high selectivities the corresponding sulfoximine-substituted homoallylic alcohols which were isolated as the silyl ethers 15a-h. Methylation of sulfoximines 15a-h afforded the aminosulfoxonium salts 5a-h which upon treatment with LiN(H)tBu gave in high yields the enantio- and diastereomerically pure silyl-substituted 2,3-dihydrofurans 4a-h. Treatment of the titanium complexes derived from the cyclic allylic sulfoximines 17a, 17b, and ent-17c with p-MeOC(6)H(4)CHO delivered with high selectivities the corresponding sulfoximine-substituted cyclic homoallylic alcohols which were isolated as the silyl ethers 18a, 18b, and ent-18c, respectively. Methylation of sulfoximines 18a, 18b, and ent-18c furnished the aminosulfoxonium salts 8a, 8b, and ent-8c, respectively, whose treatment with LiN(H)t-Bu gave the enantio- and diastereomerically pure fused bicyclic 2,3-dihydrofurans 6a, 6b, and ent-6c, respectively, in good yields. It is proposed that the 1-alkenyl aminosulfoxonium salts 5a-h, 8a, 8b, and ent-8c react with the base under alpha-elimination and formation of the acyclic and cyclic beta-silyloxy alkylidene carbenes 2a-h, 7a, 7b, and ent-7c, respectively, which then undergo a 1,5-O,Si-bond insertion and 1,2-silyl migration. The cyclic aminosulfoxonium salts 8a, 8b, and ent-8c upon treatment with 1,8-diazabicyclo[5.4.0]-7-undecene did not undergo an alpha-elimination but suffered a novel migratory cyclization with formation of the enantio- and diastereomerically pure bicyclic tetrahydrofurans 9a, 9b, and ent-9c, respectively. It is proposed that the 1-alkenyl sulfoxonium salts 8a, 8b, and ent-8c are isomerized to the allylic aminosulfoxonium salts 10a, 10b, and ent-10c, respectively, which then suffer an intramolecular substitution of the (dimethylamino)sulfoxonium group by the silyloxy group followed by a desilylation. The syntheses of the 2,3-dihydrofurans 4a-h, 6a, and 6b and of the tetrahydrofurans 9a and 9b are accompanied by the formation of sulfinamide 16 of >or=98% ee, which can be converted via sulfoxide 28 of >or=98% to the starting sulfoximine 11 of >or=98% ee.     

Über die bei hohen Ansäuerungsgraden auftretenden Polymolybdat-Typen,insbesondere zur Frage der „Dekamolybdate”︁ und „Phase C”︁-Polymolybdate

On the Polymolybdate Types Occurring at High Degrees of Acidification, with Particular Reference to the “Decamolybdates” and “Phase C” Polymolybdates It is shown that in the range of high acidification (> 1.6H⁺/MoO₄^2?) of aqueous molybdate solutions only two types of solid polymolybdates occur, namely the 36-molybdate and the “decamolybdate” types. These types can be most conveniently identified by their Raman spectra and also by some other characteristics. All the other polymolybdate types proposed in the literature for this range of acidification (“hexamolybdates”, “octamolybdates”, “dodecamolybdates”, “16-molybdates”, a 19-molybdate, the large group of polymolybdates characterized by a wide range of b in the general formula M₂O · bMoO₃ · cH₂O, “phase C” polymolybdates, a “hexagonal hydrate of molybdenum trioxide”, a “reactive molybdic acid”, “NH₃(MoO₃)₃”, and others) can be assigned to one of these two types. The most important reason for the erroneous assignments in the literature is the isomorphous exchange of varying quantities of the alkali or alkaline earth metal cations by H₃O⁺ in the crystal structure, occurring in the highly acidic solutions, particularly with the small cations. This cannot be recognized by the presently available methods of investigation and, hence, leads to the creation of new polymolybdate types. Another reason causing some of the confusion is the assignment of virtually identical X-ray diffraction data to two different types of lattices, a hexagonal and cubic lattice.     

Sulphur substituted organotin compounds : VII. Charge transfer interactions of arylthiomethyl(triphenyl)tin compounds with tetracyanoethylene

Thermolysis of η²-benzoyl(phenyl)zirconocene yields the η²-benzophenonzirconocene complex 2, isolated as a dimer. 2 exhibits an ambivalent reactivity pattern. The formation of five-membered metallacycles from 2 and olefinic hydrocarbons possibly proceeds analogous to reactions of “normal” metalolefin π-complexes. However, both reactions with the electron-deficient olefins dimethylfumarate and -maleate and the behavior towards electrophilic and protic reagents as well as aromatic hydrocarbons might be interpreted in terms of a metallaoxirane-character of 2.     

Biologisch aktive 3,3-Dimethylbicyclo[2.2.2]octane: Synthesen in der Isocamphanreihe, 35. Mitt.

Summary The bicyclo[2.2.1]- and [2.2.2]-systems are part of numerous biological active substances. Continuing our syntheses in the isocamphane series the homologous isocamphanes of mecamylamine (1 a) and of the fungicidal bicyclic compound2 were synthesized. Furthermore the syntheses ofE-homoisosantalene (15) andE,E-homoisosantalol (16) are described.

     

Einsatz der flammenlosen Atom-Absorption (Graphitrohrküvette) zur Bestimmung von Kupferspuren in Stahl und anderen Metall-Legierungen nach Extraktion

The determination of small and smallest amounts of copper in steel and other metal alloys by atomic absorption spectroscopy was investigated. It has been found, that the interferences caused by accompanying elements in the determination in aqueous solution with the flame can be completely removed by extracting the copper with Pb-DDTC in chloroform and determining this extract with the heated graphite atomizer. Moreover, it was recognised, that working with the heated graphite atomizer in organic solutions shows great advantages compared with the flame, because any solvent may be used. The methods of continuous variation by Job and the molar ratio by Yoe and Jones for the determination of the complex stoichiometry were transferred to the system Cu-DDTC by working with the heated graphite atomizer.     

Accurate determination of low pK values by (1)H NMR titration

The NMR titration methodology to determine acid dissociation constants in aqueous solutions is extended for pK(a) values between 0 and 2, where potentiometric titrations are no longer applicable. (1)H NMR spectra are acquired for single samples of constant acid concentration (e.g. 0.02M), controlled ionic strength (I=1M with HNO(3)/NaNO(3)) and varying pH. To avoid biased pH readings due to the acid error of the glass electrode, true, concentration-based pH values are deduced by combination of the charge balance equation with information from (1)H NMR chemical shifts of the investigated acid. The method has been tested on histidine (pK(1)=1.83+/-0.02) and yielded the dissociation constant of dichloroacetic acid (pK=1.06+/-0.01) for the first time with good accuracy and precision. Dichloroacetic acid is recommended as an NMR spectroscopical "indicator molecule" for in situ monitoring the pH in strong acidic solutions of other equilibrium systems.     

Fragmentation of 1-aryl-5-(2-dialkylaminovinyl)-1H-tetrazoles upon electron impact

The mass spectrometric behaviour of 1-aryl-5-(2-dialkylaminovinyI)-lH-tetrazoles was studied, especially 1-phenyl-5-(2-dimethylaminovinyl)-l H-tetrazole as a typical example of D- and ¹⁵N-labelled derivatives revealed a rearrangement via a carbodiimide-like intermediate ion.     

Infrared spectroscopic characterization of the buried interface and surfaces of bonded silicon wafers

Basic investigations have been carried out on the characterization of different processing steps in bond preparation using etched <111> faces of silicon wafers for the incidence of the infrared beam to a multiple internal reflection geometry. The method is very sensitive to the surface coverage and interface. Surface activation by RCA cleaning yields an increase of water coverage and a decrease of SiH and CH groups. The detection limit for an oxide layer between silicon wafers has been found to be about 3 nm. Received: 18 July 1997 / Revised: 15 August 1997 / Accepted: 19 August 1997