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241.
Jack E. Baldwin Alexander V.W. MaywegGareth J. Pritchard Robert M. Adlington 《Tetrahedron letters》2003,44(24):4543-4545
An expedient ten-step synthesis of a substituted tropolone is described. The synthesis involves a 3-oxidopyrylium [5+2] cycloaddition reaction with acrylonitrile as the key step, affording a highly functionalized [3.2.1]-bicycle 10 as a single regioisomer. The nitrile substituent of the reduced cycloadduct 12 permits efficient ether-bridge cleavage and tropolone 15 is obtained after a final bis-oxidation procedure. The pyranulose acetate cycloaddition precursor was derived from 3-methyl-2-furoate. 相似文献
242.
Barrett PA Boix T Puche M Olson DH Jordan E Koller H Camblor MA 《Chemical communications (Cambridge, England)》2003,(17):2114-2115
The new synthetic form of microporous crystalline silica, denoted as ITQ-12, shows a high potential for the separation of propane and propene from its mixtures. 相似文献
243.
Singh J Kronenthal DR Schwinden M Godfrey JD Fox R Vawter EJ Zhang B Kissick TP Patel B Mneimne O Humora M Papaioannou CG Szymanski W Wong MK Chen CK Heikes JE DiMarco JD Qiu J Deshpande RP Gougoutas JZ Mueller RH 《Organic letters》2003,5(17):3155-3158
[reaction: see text] An efficient asymmetric synthesis of the vasopeptidase inhibitor BMS-189921 was accomplished. Two short enantioselective syntheses of the common key intermediate (S)-alpha-aminoazepinone 6b were developed. Olefin 3 was converted to 6b via asymmetric hydrogenation. Alternatively, enyne 12 was converted to racemic alpha-aminoazepinone 15b, which was transformed to 6b by a practical dynamic resolution. 相似文献
244.
[reaction: see text] The biomimetic synthesis of the bisesquiterpenoids biatractylolide 1 and biepiasterolide 2 is reported. 相似文献
245.
[reaction: see text] The biomimetic synthesis of the racemic dimer panepophenanthrin was achieved in good yield employing a tandem reaction sequence. 相似文献
246.
Archie P. Smith Jack F. Douglas J. Carson Meredith Eric J. Amis Alamgir Karim 《Journal of Polymer Science.Polymer Physics》2001,39(18):2141-2158
Surface‐pattern formation in thin block copolymer films was investigated by utilizing a high‐throughput methodology to validate the combinatorial measurement approach and to demonstrate the value of the combinatorial method for scientific investigation. We constructed measurement libraries from images of subregions of block copolymer films having gradients in film thickness and a range of molecular mass, M. A single gradient film covers a wide range of film morphologies and contains information equivalent to a large number of measurements of films having a fixed thickness, h. Notably, the scale of the surface patterns is generally much larger than the molecular dimensions so that the interpretation of the patterns is more subtle than ordering in bulk block copolymer materials, and there is no predictive theory of this type of surface‐pattern formation. We observed a succession of surface patterns that repeat across the film with increasing h [extended smooth regions, regions containing circular islands, labyrinthine (“spinodal”) patterns, holes, and smooth regions again]. The extended smooth regions and the labyrinthine patterns appear to be novel features revealed by our combinatorial study, and these patterns occurred as bands of h that were quantized by integral multiples of the bulk lamellar period, Lo. The magnitude of the height gradient influenced the width of the bands, and the smooth regions occupied an increasing fraction of the film‐surface area with an increasing film gradient. The average size of the spinodal patterns, λ, was found to scale as λ ~ L or λ ~ M?1.65 and reached a limiting size at long annealing times. The hole and island features had a size comparable to λ, and their size likewise decreased with increasing M. The smooth regions were attributed to an increase in the surface‐chain density in the outer brushlike block copolymer layer with increasing h, and the scaling of λ with M was interpreted in terms of the increasing surface elasticity with M. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2141–2158, 2001 相似文献
247.
248.
Let be a graph with diameter d 2. Recall is 1-homogeneous (in the sense of Nomura) whenever for every edge xy of the distance partition{{z V() | (z, y) = i, (x, z) = j} | 0 i, j d}is equitable and its parameters do not depend on the edge xy. Let be 1-homogeneous. Then is distance-regular and also locally strongly regular with parameters (v,k,,), where v = k, k = a
1, (v – k – 1) = k(k – 1 – ) and c
2 + 1, since a -graph is a regular graph with valency . If c
2 = + 1 and c
2 1, then is a Terwilliger graph, i.e., all the -graphs of are complete. In [11] we classified the Terwilliger 1-homogeneous graphs with c
2 2 and obtained that there are only three such examples. In this article we consider the case c
2 = + 2 3, i.e., the case when the -graphs of are the Cocktail Party graphs, and obtain that either = 0, = 2 or is one of the following graphs: (i) a Johnson graph J(2m, m) with m 2, (ii) a folded Johnson graph J¯(4m, 2m) with m 3, (iii) a halved m-cube with m 4, (iv) a folded halved (2m)-cube with m 5, (v) a Cocktail Party graph K
m × 2 with m 3, (vi) the Schläfli graph, (vii) the Gosset graph. 相似文献
249.
Khandelwal P Dementyev AE Kuzma NN Barrett SE Pfeiffer LN West KW 《Physical review letters》2001,86(23):5353-5356
Optically pumped nuclear magnetic resonance measurements of 71Ga spectra were carried out in an n-doped GaAs/Al(0.1)Ga0.9As multiple quantum well sample near the integer quantum Hall ground state nu = 1. As the temperature is lowered (down to T approximately 0.3 K), a "tilted plateau" emerges in the Knight shift data, which is a novel experimental signature of quasiparticle localization. The dependence of the spectra on both T and nu suggests that the localization is a collective process. The frozen limit spectra appear to rule out a 2D lattice of conventional Skyrmions. 相似文献
250.
Let {C
i}
0 be a sequence of independent and identically distributed random variables with vales in [0, 4]. Let {X
n}
0 be a sequence of random variables with values in [0, 1] defined recursively by X
n+1=C
n+1
X
n(1–X
n). It is shown here that: (i) E ln C
1<0X
n0 w.p.1. (ii) E ln C
1=0X
n0 in probability (iii) E ln C
1>0, E |ln(4–C
1)| such that (0, 1)=1 and is invariant for {X
n}. (iv) If there exits an invariant probability measure such that {0}=0, then E ln C
1>0 and – ln(1–x) (dx)=E ln C
1. (v) E ln C
1>0, E |ln(4–C
1)|< and {X
n} is Harris irreducible implies that the probability distribution of X
n converges in the Cesaro sense to a unique probability distribution on (0, 1) for all X
00. 相似文献