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991.
992.
Hatice Mutlu Michael A. R. Meier 《Journal of polymer science. Part A, Polymer chemistry》2010,48(24):5899-5906
The ring‐opening metathesis polymerization (ROMP) of fatty acid functionalized norbornenes was explored in the presence of dichloro[1,3‐bis(2,4,6‐trimethylphenyl)‐2‐imidazolidinylidene](benzylidene)bis(3‐bromopyridine)ruthenium(II) ( C3 ) at room temperature. The investigated monomers were derived from fatty acids with different chain lengths (C6, C8, C10, C12, C14, C16, and C18) and can therefore contribute to the development of more sustainable, bio‐based polymeric materials. The polymerizations initiated by C3 proceeded in a living fashion with good initiation efficiency, and thus the synthesis of well‐defined polymers with narrow polydispersities was accomplished. All prepared polymers were fully characterized (GPC, DSC, TGA, NMR) and the results of these investigations are discussed within this contribution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
993.
K. B. Sophy Dr. Jer‐Lai Kuo Prof. Dr. Xue‐Wei Liu Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(2):588-594
We carried out a principle study on the reaction mechanism of rhodium‐catalyzed intramolecular aziridination and aziridine ring opening at a sugar template. A sulfamate ester group was introduced at different positions of glycal to act as a nitrene source and, moreover, to allow the study of the relative reactivity of the nitrene transfer from different sites of the glycal molecule. The structural optimization of each intermediate along the reaction pathway was extensively done by using BPW91 functional. The crucial step in the reaction is the Rh‐catalyzed nitrene transfer to the double bond of the glycal. We found that the reaction could proceed in a stepwise manner, whereby the N atom initially induced a single‐bond formation with C1 on the triplet surface or in a single step through intersystem crossing (ISC) of the triplet excited state of the rhodium–nitrene transition state to the singlet ground state of the aziridine complexes. The relative reactivity for the conversion of the nitrene species to the aziridine obtained from the computed potential energy surface (PES) agrees well with the reaction time gained from experimental observation. The aziridine ring opening is a spontaneous process because the energy barrier for the formation of the transition state is very small and disappears in the solution calculations. The regio‐ and stereoselectivity of the reaction product is controlled by the electronic property of the anomeric carbon as well as the facial preference for the nitrene insertion, and the nucleophilic addition. 相似文献
994.
Jan Bornholdt Dr. Jakob Felding Dr. Rasmus P. Clausen Dr. Jesper L. Kristensen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(41):12474-12480
The pyrimidine‐2‐sulfonyl (pymisyl) group is introduced as a new protecting group that can be used to activate aziridines towards ring opening. It is readily introduced and removed under mild conditions. Regioselective ring opening of pymisyl‐protected 2‐methyl‐aziridine with organocuprates gives the corresponding sulfonamides in high yields, and the pymisyl group can subsequently be removed upon treatment with a thiolate. The versatility of this new nitrogen protecting group is illustrated with a new synthesis of Selegiline, a monoamine oxidase‐B inhibitor marketed for the treatment of Parkinson’s disease. 相似文献
995.
Dihydroxyoligophenylenes (HO-ArPh(m)-OHs) with 9,9-dihexyl-2,7-fluorene (Ar=Flu), 2,5-dioctyloxy-1,4-benzene (Ar=Dob), pyridine (Ar=Py), or thiophene (Ar=Th) rings were synthesized by the Suzuki coupling reaction. Absorption maxima (λmax) of HO-ArPh(m)-OHs shifted progressively toward long wavelengths due to the expansion of the π-conjugation system with an increase in the number of benzene rings. Deprotonation of the OH groups of HO-ArPh(m)-OHs by treatment with NaH caused a bathochromic shift of λmax. The bathochromic shift of the deprotonated species increased with the donor numbers (DNs) of the solvents. The emission peak positions of NaO-ArPh(m)-ONas depended on the DNs of the solvents; therefore, the emission color could be tuned by changing the solvent. 相似文献
996.
Tomas Lebl 《Tetrahedron》2010,66(51):9694-9702
Variable temperature NMR analysis and computational methods have been used to develop a detailed understanding of the 1H NMR spectra of a family of medium-sized ring containing compounds. The family consists of analogues containing 10-, 11- and 12-membered rings and in all cases the NMR spectra at room temperature showed a series of diastereotopic methylene signals despite the lack of a stereogenic centre in these systems. On repeating the NMR analysis at higher temperatures, all the signals coalesced for the 12-membered ring system consistent with full interconversion of ring conformers. This was not observed in the analogous 10- and 11-membered ring systems with the interchange of conformers remaining slow on the NMR timescale. However, 1D gs-NOESY/EXSY NMR experiments showed that in the smaller ring systems interconversion of diastereotopic protons did occur. Computational studies suggest that the dynamic process observed by NMR for the 10- and 11-membered rings systems is different from that observed in the 12-membered ring containing compound. 相似文献
997.
Xianjie Fang 《Tetrahedron letters》2010,51(2):317-8716
A domino sequence of cyclization of 1,6-enyne with 2-bromoarylaldehyde followed by the intramolecular Aldol-condensation has been realized in the presence of 5 mol % of palladium catalyst. This sequence provides a convenient protocol to access polycyclic ring systems with readily available starting materials under simple Pd(0)-catalyzed conditions. The intramolecular Aldol-condensation has been proposed as the key step for the catalytic cycle. 相似文献
998.
Burkhardt I. Wilke 《Tetrahedron letters》2010,51(52):6871-6873
Derivatives of camphorsultam which contain novel spirooxazolidine and spirooxazine structures have been prepared in high yield and purity. Though it was expected that the ketone moiety would undergo acetal formation, the imine instead underwent reaction and was proven by X-ray crystallography and 2D NMR techniques. The initial ketone-containing derivatives were then reduced to produce exo-hydroxy analogs that have potential as a new family of chiral auxiliaries. 相似文献
999.
1000.