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71.
Ulrich Schllkopf 《Angewandte Chemie (International ed. in English)》1977,16(6):339-348
Being both nucleophilic and electrophilic, α-metalated isocyanides can add to polar double bonds, forming heterocycles. They are also synthons for α-metalated primary amines. This article describes recent or improved procedures for their use in organic synthesis: (1) In heterocyclic syntheses to give 2-oxazolines, 2-imidazolines, 2-thiazolines, oxazoles and oligooxazoles, thiazoles, triazoles, imidazolinones, pyrroles, 5,6-dihydro-1,3-oxazines and -thiazines, and (via cycloaddition with nitrones) 2-imidazolidinones. (2) In the field of formylaminomethylenation, for example transformation of estrone methyl ether and a keto sugar into the corresponding α-formylaminoacrylic esters, and the conversion of aldehydes and ketones by 3- and 4-pyridyl-methyl isocyanides into N-(1-pyridyl-1-alkenyl)formamides and their hydrolysis to 3- and 4-acylpyridines. (3) In connection with the use of α-metalated isocyanides as synthons for α-metalated primary amines, the author demonstrates how they may be used for preparation of 1,2- and 1,3-amino alcohols, 1,2-diamines, 2,3-diaminoalkanoic acids and for synthesis of higher amino acids starting from simple amino acids. 相似文献
72.
Cyclisation of the title compounds leads to mixtures of the expected 4H-cyclopental[b]pyrrol-4-ones (1), the corresponding 6-ones (3) by a single rearrangement, and the cyclopenta[c]pyrrol-4-ones (4) by a double rearrangement, the proportions depending upon the substituents.The 1H NMR spectra of 2-methyl-4H-cyctopenta[b]thiophen-6-one (3f) shows 6J long range coupling, but this is absent in the corresponding pyrroles (3c,d). The 13C spectra of 1 and 3 cannot be interpreted on the basis of substituent chemical shifts in pyrroles and thiophens, and are clearly -CH = CH-X (X = NMe, NPh, S) bridged derivatives of cyclopent-2-enone. 相似文献
73.
The complexation equilibria between Ni(II) and Zn(II) metal ions with 3-(1-naphthyl)-2-mercaptopropenoic acid (H2NMP) were studied by glass electrode potentiometry, at 25 °C and 1.0 mol·dm–3 in NaClO4 as constant ionic medium in 50% (v/v) water-ethanol solutions. Formation constants for the complexes Ni(NMP), Ni(NMP)
2
2–
, Zn(NMP) and Zn(NMP)
2
2–
, refined by the MINIGLASS program, are reported. 相似文献
74.
Alain-Sol Sznitman 《Probability Theory and Related Fields》1996,105(1):31-56
Summary We continue our study ofd-dimensional Brownian motion in a soft repulsive Poissonian potential over a long time interval [0,t]. We prove here a pinning effect: for typical configuratons, with probability tending to 1 ast tends to , the particle gets trapped close to locations of near minima of certain variational problems. These locations lie at distances growing almost linearly witht from the origin, and the particle gets pinned within distance smaller than any positive power oft of one such location. In dimension 1, we can push further our estimates and show that in a suitable sense, the particle gets trapped with high probability, within time t and within distance (logt)2+ from a suitable location at distance of ordert/(logt)3 from the origin.This article was processed by the author using the LATEX style filepljour1m from Springer-Verlag 相似文献
75.
Stationary processes of k-flats in
d
can be thought of as point processes on the Grassmannian
k
d
of k-dimensional subspaces of
d
. If such a process is sampled by a (d–k+ j)-dimensional space F, it induces a process of j-flats in F. In this work we will investigate the possibility of determining the original k-process from knowledge of the intensity measures of the induced j-processes. We will see that this is impossible precisely when 1<k<d–1 and j=0,...,2[r/2]–1, where r is the rank of the manifold
k
d
. We will show how the problem is equivalent to the study of the kernel of various integral transforms, these will then be investigated using harmonic analysis on Grassmannian manifolds.The research of the first and third authors was supported in part by NSF grants DMS-9207019 and DMS-9304284. The research of the second author was supported in part by NFR contract number R-RA 4873-306 and the Swedish Academy of Sciences. 相似文献
76.
Yong Zhang 《Order》1996,13(4):365-367
G. Grätzer, H. Lakser, and E. T. Schmidt proved that every distributive lattice with n join-irreducible elements can be represented as the congruence lattice of a small lattice L, that is, a lattice L with O(n
2
) elements. G. Grätzer, I. Rival, and N. Zaguia proved that, for any <2, O(n
2
) can not be improved to O(n
). In this note we show that the theorem about small representation can be improved further to get a more delicate result. 相似文献
77.
The property of self-adjointness of the operatorQ =a
+ +a
- in three types ofq-oscillator algebras is considered. Spectral measures and generalized eigenfunctions ofQ are found in the cases when this operator is bounded. Generalized eigenvectors are expressed in terms ofq-Hermite polynomials. If the operatorQ is unbounded, then its closure
is not self-adjoint. However, in this case,
admits self-adjoint extensions. Deficiency subspaces are one-dimensional. These subspaces are explicitly found. 相似文献
78.
Richard Steiner 《Applied Categorical Structures》1993,1(3):247-284
The theory of directed complexes is a higher-dimensional generalisation of the theory of directed graphs. In a directed graph, the simple directed paths form a subset of the free category which they generate; if the graph has no directed cycles, then the simple directed paths constitute the entire category. Generalising this, in a directed complex there is a class of split subsets which is contained in and generates a free -category; when a simple loop-freeness condition is satisfied, the split sets constitute the entire -category. The class of directed complexes is closed under the natural product and join constructions. The free -categories generated by directed complexes include the important examples associated to cubes and simplexes. 相似文献
79.
Israel Gohberg Naum Krupnik Ilya Spitkovsky 《Integral Equations and Operator Theory》1993,17(3):322-337
The Banach algebra generated by one-dimensional linear singular integral operators with matrix valued piecewise continuous coefficients in the spaceL
p
(,) with an arbitrary weight is studied. The contour consists of a finite number of closed curves and open arcs with satisfy the Carleson condition. The contour may have a finite number of points of selfintersection. The symbol calculus in this algebra is the main result of the paper. 相似文献
80.
The hydrolysis reaction of
,
and
,
-dipalmitoylphosphatidylcholine (DPPC) catalized by bee venom phospholipase A2 was studied in spreading monolayer at the water/air interface. DPPC and the hydrolysis products, palmitic acid and
-lysophosphatidylcholine, palmitoyl were characterized at the interface by means of surface pressure, surface potential and ellipsometric measurements. Furthermore, mixed monolayers of reagents and products were investigated to ascertain their miscibility. The results show that the hydrolysis reaction can be followed by the decrease of surface pressure with time on subphases containing β-cyclodextrin, a well-known complexing agent of many amphiphilic compounds. The order of the reaction, the kinetic constant and other kinetic parameters are deduced. 相似文献