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61.
A new method for the preparation of alpha-chlorodifluoromethyl-, alpha-bromodifluoromethyl-, and alpha-difluoromethyl-substituted alpha-hydroxy and alpha-amino acid esters 11, 19-21 is described. The key step of the synthesis is the regioselective alkylation of ketones 5, 7-9 and imines 16-18 with C-nucleophiles. The ketones 7-9 are readily available from 3,3,3-trifluorolactate 1 by a five-step procedure. Subsequent removal of the protecting groups from 19-21 provides the corresponding free amino acids 25, 26, 28.  相似文献   
62.
On singlet excitation (λ = 254 nm, THF, pentane or hexane), the diastereoisomeric methano-epoxydienes (E)- 6 and (E)- 7 undergo interconversion and yield the products 8 – 11 . The main process is the cleavage of the oxirane ring to the vinyl carbene intermediate e which undergoes addition to the adjacent double bond furnishing the cyclopropene 8 . The alternative carbene intermediate f is evidenced by the formation of the cyclobutene 10 . For the fragmentation leading to 11 , the carbene f as well as the dipolar species h are considered as possible intermediates. On triplet sensitization (acetone, λ > 280 nm), (E)- 7 shows behavior typical of epoxydienes, undergoing fission of the C? O bond of the oxirane ring and isomerization to the compounds 13 , 14 and (E/Z)- 15 .  相似文献   
63.
The invariance principle for ϕ-mixing sequences   总被引:1,自引:0,他引:1  
Summary In this paper we investigate the invariance principle for -mixing sequences, satisfying restrictions on the variances which are a weak form of stationarity. No mixing rate is assumed. For -mixing strictly stationary sequences we give a necessary and sufficient condition for the invariance principle.  相似文献   
64.
The utility of the aminonitrile 1 as an educt for the preparation of several new examples of heterocyclefused pyridazines (the [1,2,4]triazolo[1′,5′:1,6]pyrimido[4,5-c]pyridazine 7 , the pyrimido[4,5-c]pyridazines 8, 10a,b , and the pyrido[2,3-c]pyridazine 11 ) is demonstrated.  相似文献   
65.
Identification of cis/trans isomers of unsaturated fatty acids cannot usually be achieved by GC-MS (gas chromatography-mass spectrometry) without reference substances. In this study a GC-FTIR-MS system (gas chromatography-Fourier transform-mass spectrometry) was used to identify fatty acid methyl esters (FAMEs) and differentiate between the cis/trans isomers. Besides methyl esters, 2-alkenyl-4,4-dimethyloxazoline derivatives (DMOX), which have been used to locate double bond positions of unsaturated fatty acids, were examined with respect to their suitability for cis/trans differentiation. A combined GC-FTIR-MS system with a wide band (4000–550 cm?1) mercury cadmium telluride (MCT) detector was used in series and parallel to identify 31 reference unsaturated fatty acids, including 7 pairs of cis/trans isomers. Serum samples of healthy persons and commercially available fish oil were analyzed as examples of complex mixtures. Using splitless injection the detection limit for the less sensitive IR detector was 25 ng/μl in case of the weak cis and trans bands. In the FTIR spectra cis/trans isomers were identified by analysis of bands arising from C? H out-of-plane (oop) bending: for both the FAME and DMOX derivatives cis-1,2-disubstituted double bonds give a strong band near 720 cm?1 and the corresponding trans isomers near 967 cm?1. cis Isomers could be identified further by a band at 3012 cm?1. With the combined data of the GC-FTIR-MS system it is now possible to identify polyunsaturated fatty acids with regard to the discrimination of cis/trans isomers.  相似文献   
66.
The azacyclopentadienyl compounds (2,5-C4tBu2RHN)MCl3 (M = Ti, Zr, Hf; R = H, SiMe3) have been prepared as stable solids from the lithiated pyrroles and MCl4. The π-coordination of the azacyclopentadienyl ligands, as suggested from 13 C NMR data, has been confirmed for (2,5-C4tBu2H2N)TiCl3 by an X-ray diffraction study.  相似文献   
67.
The enantioselective conjugate addition of diethylzinc to the activated nitroolefin methyl 3-nitropropenoate is efficiently catalyzed by copper(I) complexes with BINOL-based enantiopure phosphoramidite ligands. The nitroolefin moiety acts as the predominant Michael acceptor, giving rise to the unambiguous formation of 2-alkyl-3-nitro-propanoates. Moderate to excellent enantioselectivities and high chemical yields are obtained. The product can easily be transformed into a beta(2)-homoamino acid. [reaction--see text]  相似文献   
68.
We prove finiteness results of Plateau's problem for boundary curves in a normal chart of radius R < /2 in an analytic Riemannian manifold. It is shown that for analytic there exist only finitely many minimal surfaces of the type of the disc bounded by , which represent an absolute minimum of area, and if boundary branch points are excluded, there exist only finitely many relative minima in the normal chart. If lies on the boundary of a strict convex manifold, there cannot exist any boundary branch points.

Die vorliegende Arbeit entstand als Dissertation am Mathematischen] Institut der Universität Saarbrücken.

Herrn Prof. Dr. F. Tomi möchte ich für die Bereitstellung des Themas und für seine Betreuung sehr herzlich danken.  相似文献   
69.
The organoaluminium and -gallium hydroxylamides (Me2GaONMe2)2, (tBu2AlONMe2)2, (tBu2GaONMe2)2 and (Me2AlONiPr2)2 have been prepared by the reaction of the hydroxylamines Me2NOH and iPr2NOH with the trialkylmetal compounds trimethylgallium, tri-tbutylaluminium and tri-tbutylgallium, respectively. All compounds have been characterised by NMR spectroscopy (1H, 13C, 15N, 17O and 27Al), by mass spectrometry and elemental analyses. The crystal structures of the four compounds have been determined, showing that they all form dimers but with different modes of aggregation: (Me2GaONMe2)2 has a Ga2O2N2 six-membered ring, (tBu2AlONMe2)2 and (Me2AlONiPr2)2 have Al2O2 four-membered rings, (tBu2GaONMe2)2 forms a Ga2O2N five-membered ring.  相似文献   
70.
2‐Iminoimidazolines — Strong Nitrogen Bases als Ligands in Inorganic Chemistry Due to the tendency of the 5‐membered cyclic fragment to accept a positive charge which yields an ylide type bonding situation, 2‐iminoimidazolines are strong nitrogen bases. They can serve as neutral ligands being 2+2 electron donors. Deprotonation leads to the anions which are potential 2+4 electron donors. We describe first the synthesis and characterization of the title compound 2‐imino‐1, 3‐dimethylimidazoline (ImNH, 8 ) and its anion 9 . Next we demonstrate their properties as ligands in complexes of main group elements and transition metals. In a third chapter we describe attempts to functionalize iminoimidazolines with the goal to create neutral ligands that coordinate in a semistable fashion. On this way we want to make a contribution to the chemistry of complex compounds directed towards catalysis.  相似文献   
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