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101.
Dr. Malte Brasholz Dr. James M. Macdonald Dr. Simon Saubern Dr. John H. Ryan Prof. Dr. Andrew B. Holmes 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(37):11471-11480
The total synthesis of the spiropiperidine alkaloid (?)‐perhydrohistrionicotoxin (perhydro‐HTX) 2 has been accomplished on a gram scale by employing both conventional batch chemistry as well as microreactor techniques. (S)‐(?)‐6‐Pentyltetrahydro‐pyran‐2‐one 8 underwent nucleophilic ring opening to afford the alcohol 10 , which was elaborated to the nitrone 13 . Protection of the nitrone as the 1,3‐adduct of styrene and side‐chain extension to the unsaturated nitrile afforded a precursor 17 , which underwent dipolar cycloreversion and 1,3‐dipolar cycloaddition to give the core spirocyclic precursor 18 that was converted into perhydro‐HTX 2 . The principal steps to the spirocycle 18 have successfully been transferred into flow mode by using different types of microreactors and in a telescoped fashion, allowing for a more rapid access to the histrionicotoxins and their analogues by continuous processing. 相似文献
102.
Philipp Zacharias Dr. Malte C. Gather Dr. Anne Köhnen Dr. Nina Rehmann Klaus Meerholz Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(22):4038-4041
Enlightening the memory : The integration of a crosslinkable photochromic dithienylperfluorocyclopentene (DTE) into organic light‐emitting diodes (OLED) allows for the individualization of the emissive area of the OLED device, for example, for signage applications. The operation principle is based on switching the injection barrier for holes (positive charge carriers). Very large ON/OFF ratios of up to 3000 for current as well as electroluminescence have been achieved.
103.
Manufacturers in a wide range of industries nowadays face the challenge of providing a rich product variety at a very low cost. This typically requires the implementation of cost efficient, flexible production systems. Often, so called mixed-model assembly lines are employed, where setup operations are reduced to such an extent that various models of a common base product can be manufactured in intermixed sequences. However, the observed diversity of mixed-model lines makes a thorough sequence planning essential for exploiting the benefits of assembly line production. This paper reviews and discusses the three major planning approaches presented in the literature, mixed-model sequencing, car sequencing and level scheduling, and provides a hierarchical classification scheme to systematically record the academic efforts in each field and to deduce future research issues. 相似文献
104.
105.
In a mixed-model assembly line, varying models of the same basic product are to be produced in a facultative sequence. This results to a short-term planning problem where a sequence of models is sought which minimizes station overloads. In practice – e.g. the final assembly of cars – special sequencing rules are enforced which restrict the number of models possessing a certain optional feature k to rk within a subsequence of sk successive models. This problem is known as car sequencing. So far, employed solution techniques stem mainly from the field of Logic and Constraint Logic Programming. In this work, a special Branch & Bound algorithm is developed, which exploits the problem structure in order to reduce combinatorial complexity. 相似文献
106.
Brian H. Davison Sadie R. Drescher Gerald A. Tuskan Mark F. Davis Nhuan P. Nghiem 《Applied biochemistry and biotechnology》2006,130(1-3):427-435
Wood samples from second generation Populus cross were shown to have different lignin contents and S/G ratios (S: syringyl-like lignin structures; G: guaiacyl-like lignin
structures). The lignin contents varied from 22.7% to 25.8% and the S/G ratio from 1.8 to 2.3. Selected samples spanning these
ranges were hydrolyzed with dilute (1%) sulfuric acid to release fermentable sugars. The conditions were chosen for partial
hydrolysis of the hemicellulosic fraction to maximize the expression of variation among samples. The results indicated that
both lignin contents and S/G ratio significantly affected the yield of xylose. For example, the xylose yield of the 25.8%
lignin and 2.3 S/G (hihg lignin, high S/G) sample produced 30% of the theoretical yield, whereas the xylose yield of the 22.7%
lignin and 1.8 S/G (low lignin, low S/G) was 55% of the theoretical value. These results indicate that lignin content and
composition among genetic variants within a single species can influence the hydrolyzability of the biomass. 相似文献
107.
1,4‐Di(isopropyl)‐1,4‐diazabutadiene as a Reagent for the Trapping of Monomeric Fragments of the Tetragalliumcluster Ga4[C(SiMe3)3]4 – Formation of an Unsaturated GaN2C2 Heterocycle and an Oxidation Product Containing a Ga‐O‐O‐Ga Group The tetrahedral tetragallium cluster Ga4[C(SiMe3)3]4 ( 1 ) dissociates upon dissolution to yield the monomeric fragments Ga‐R [R = C(SiMe3)3]. These monomers could be trapped now by the treatment of their solutions with 1,4‐di(isopropyl)‐1,4‐diazabutadiene. The product of the cycloaddition reaction ( 2 ) possesses a five‐membered GaN2C2 heterocycle with a coordinatively unsaturated gallium atom and an endocyclic C=C double bond. 2 is rather sensitive towards oxidation by traces of air. The contact with oxygen yielded a digallium peroxide [(C2N2iPr2)RGa‐O‐O‐GaR(C2N2iPr2)] ( 3 ) which was isolated in a very low yield only and which has a gallium atom attached to each oxygen atom of the inner peroxo group. Both chelating ligands of 3 possess an unpaired electron. 相似文献
108.
Malte Fischer Manfred Manßen Marc Schmidtmann Thorsten Klüner Rüdiger Beckhaus 《Chemical science》2021,12(41):13711
The reaction of the titanium imido complex 1b with 2-butyne leads to the formation of the titanium azadiene complex 2a at ambient temperature instead of yielding the archetypical [2 + 2] cycloaddition product (titanaazacyclobutene) which is usually obtained by combining titanium imido complexes and internal alkynes. The formation of 2a is presumably caused by an initial propargylic C(sp3)–H activation step and quantum chemical calculations suggest that the outcome of this unexpected reactivity is thermodynamically favored. The previously reported titanaazacyclobutene I (which is obtained by reacting 1b with 1-phenyl-1-propyne) undergoes a rearrangement reaction at elevated temperature to give the corresponding five-membered titanium azadiene complex 2b.An unexpected reactivity between a titanium imido complex and internal alkynes was unveiled yielding titanaazacyclobutenes instead of the expected [2 + 2] cycloaddition products. 相似文献
109.
C. Herberg M. Ostrick H.G. Andresen J.R.M. Annand K. Aulenbacher J. Becker P. Drescher D. Eyl A. Frey P. Grabmayr S.J. Hall P. Hartmann T. Hehl W. Heil J. Hoffmann D. Ireland J.D. Kellie F. Klein K. Livingston Ch. Nachtigall A. Natter E.W. Otten R.O. Owens E. Reichert D. Rohe H. Schmieden R. Sprengard M. Steigerwald K.-H. Steffens Th. Walcher R. Watson 《The European Physical Journal A - Hadrons and Nuclei》1999,5(2):131-135
The electric form factor of the neutron G
E,n has been determined at the Mainz Microtron MAMI at the low momentum transfer Q
2= 0.15 (GeV/c)2 in a measurement of the recoil polarisation ratio P
x/Pz in the quasifree reaction D(e,e′n)p. At this Q
2 the influence of the nuclear binding is strong. A purely kinematical model is used to get some insight into the effect of
the initial Fermi momentum distribution of the neutron. The influence of the final state interaction is determined quantitatively
by a model of Arenh?vel et al.. After the corresponding corrections a value of G
E,n(0.15 (GeV/c)2) = 0.0481±0.0065stat±0.0053syst is obtained.
Received: 12 April 1999 相似文献
110.