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261.
Easy two‐step synthesis of a series of dithiines was performed from succinic anhydride via cyclization of the corresponding 4‐(alkylamino)‐4‐oxobutanoic acids (succinamic acids). The reaction, carried out in polar aprotic solvents, gave 4,8‐dithiine‐indacene‐1,3,5,7‐tetraones (diimides 3) via 3,7‐bis‐4,8‐dithia‐indacene‐1,5‐diones (diisoimides 2), which could be isolated. Surprisingly, in this reaction, thionyl chloride appeared as an oxidant, and this process seemed to be useful for the syntheses of S‐containing heterocyclic compounds such as 1,4‐dithiins. A mechanistic pathway was considered. 相似文献
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263.
The direct coupling of aryl halides with thiophene would be a considerable advantage for sustainable development because of only HBr associated with a base as by-product is formed and the number of steps to prepare these compounds is less than in more classical coupling reactions. We observed that through the use of only 0.2 mol% Pd(OAc)2 as the catalyst, a range of aryl bromides undergoes coupling via a C-H bond activation/functionalization reaction with thiophene to give 2-arylated thiophenes in good yields. In most cases, only traces of polyarylated thiophenes were detected when a large excess of thiophene was employed. This air-stable catalyst can be used with a wide variety of aryl bromides. 相似文献
264.
Gregory Von White II Roger L. Clough James M. Hochrein Robert Bernstein 《Polymer Degradation and Stability》2013
Nylon 6.6 containing 13C isotopic labels at specific positions along the macromolecular backbone has been subjected to extensive thermal-oxidative aging at 138 °C for time periods up to 243 days. In complementary experiments, unlabeled Nylon 6.6 was subjected to the same aging conditions under an atmosphere of 18O2. Volatile organic degradation products were analyzed by cryofocusing gas chromatography mass spectrometry (cryo-GC/MS) to identify the isotopic labeling. The labeling results, combined with basic considerations of free radical reaction chemistry, provided insights to the origin of degradation species, with respect to the macromolecular structure. A number of inferences on chemical mechanisms were drawn, based on 1) the presence (or absence) of the isotopic labels in the various products, 2) the location of the isotope within the product molecule, and 3) the relative abundance of products as indicated by large differences in peak intensities in the gas chromatogram. The overall degradation results can be understood in terms of free radical pathways originating from initial attacks on three different positions along the nylon chain which include hydrogen abstraction from: the (CH2) group adjacent to the nitrogen atom, at the (CH2) adjacent the carbonyl group, and direct radical attack on the carbonyl. Understanding the pathways which lead to Nylon 6.6 degradation ultimately provides new insight into changes that can be leveraged to detect and reduce early aging and minimize problems associated with material degradation. 相似文献
265.
Shaoming Duan Edith R. Binkley Roger W. Binkley 《Journal of carbohydrate chemistry》2013,32(7):1029-1034
Abstract In 1968 Zen and coworkers reported that thep-tolylsulfonyl group could be removed from carbohydrate systems by photochemical reaction (eq 1).1 Since then other investigators have used this deprotection process in carbohydrate synthesis.2-10 Mechanistic studies11-16 have shown that tosylate photolysis is promoted by compounds (e.g., triethylamine) that donate an electron to an excitedp-toluenesulfonate to generate a radical anion (1). This intermediate then fragments to form the anion of the deprotected sugar (Scheme 1). Since generating a radical anion is the central element in this photochemical process, structural changes that impact radical anion formation should influence the reaction. Replacing the p - tolylsulfonyl group with the pentafluorophenylsulfonyl group generates a more stable radical anion (2) because the electronegative fluorine atoms can help stabilize the negative charge. Since we have a continuing interest in the photochemistry of sulfonic acid esters, we synthesized the pentafluorobenzenesulfonates (pentaflates) 3-6 and studied their photochemistry under electron transfer conditions. 相似文献
266.
Dr. Ulrich F. J. Mayer Elliot Murphy Dr. Mairi F. Haddow Prof. Michael Green Prof. Roger W. Alder Prof. Duncan F. Wass 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(13):4287-4299
We make the case for benzo[c]quinolin‐6‐ylidene ( 1 ) as a strongly electron‐donating carbene ligand. The facile synthesis of 6‐trifluoromethanesulfonylbenzo[c]quinolizinium trifluoromethanesulfonate ( 2 ) gives straightforward access to a useful precursor for oxidative addition to low‐valent metals, to yield the desired carbene complexes. This concept has been achieved in the case of [Mn(benzo[c]quinolin‐6‐ylidene)(CO)5]+ ( 15 ) and [Pd(benzo[c]quinolin‐6‐ylidene)(PPh3)2(L)]2+ L=THF ( 21 ), OTf ( 22 ) or pyridine ( 23 ). Attempts to coordinate to nickel result in coupling products from two carbene precursor fragments. The CO IR‐stretching‐frequency data for the manganese compound suggests benzo[c]quinolin‐6‐ylidene is at least as strong a donor as any heteroatom‐stabilised carbene ligand reported. 相似文献
267.
In this paper, we study bimodules over a von Neumann algebra M in the context of an inclusion M⊆M?αG, where G is a discrete group acting on a factor M by outer ?-automorphisms. We characterize the M -bimodules X⊆M?αG that are closed in the Bures topology in terms of the subsets of G . We show that this characterization also holds for w?-closed bimodules when G has the approximation property (AP ), a class of groups that includes all amenable and weakly amenable ones. As an application, we prove a version of Mercer's extension theorem for certain w?-continuous surjective isometric maps on X. 相似文献
268.
Conditions are described for one-pot Brønsted acid and organocatalysed enantioselective α-amination of acetals and associated functionalities. Of the organocatalysts screened, proline tetrazole gave the highest ee, while aqueous monochloroacetic acid proved to be the best Brønsted acid activator regarding minimizing racemization and maximizing product yield. The reaction opens up the way for using masked carbonyl functionalities in organocatalysis. 相似文献
269.
270.