- Side-chain Effects on the Fragmentation Behaviour of Alkylthiophenes
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The processes leading to the fragment ions formed from alkylthiophene molecule ions by benzylic cleavage without and with transfer of one hydrogen from the side-chain to the ring and the influence of additional methyl groups on the relative importance of these two fragmentation reactions were investigated.
- Lange, D.,Budzikiewicz, H.
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- Catalyst-Controlled Selective Functionalization of Unactivated C-H Bonds in the Presence of Electronically Activated C-H Bonds
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A new chiral dirhodium tetracarboxylate catalyst, Rh2(S-2-Cl-5-BrTPCP)4, has been developed for C-H functionalization reactions by means of donor/acceptor carbene intermediates. The dirhodium catalyst contains four (S)-1-(2-chloro-5-bromophenyl)-2,2-diphenylcyclopropane-1-carboxylate ligands, in which all four 2-chloro-5-bromophenyl groups are on the same face of the catalyst, leading to a structure, which is close to C4 symmetric. The catalyst induces highly site selective functionalization of remote, unactivated methylene C-H bonds even in the presence of electronically activated benzylic C-H bonds, which are typically favored using earlier established dirhodium catalysts, and the reactions proceed with high levels of diastereo- and enantioselectivity. This C-H functionalization method is applicable to a variety of aryl and heteroaryl derivatives. Furthermore, the potential of this methodology was illustrated by sequential C-H functionalization reactions to access the macrocyclic core of the cylindrocyclophane class of natural products.
- Liu, Wenbin,Ren, Zhi,Bosse, Aaron T.,Liao, Kuangbiao,Goldstein, Elizabeth L.,Bacsa, John,Musaev, Djamaladdin G.,Stoltz, Brian M.,Davies, Huw M. L.
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- Synthesis and self-assembly of 5,5′-bis(phenylethynyl)-2,2′-bithiophene-based bolapolyphiles in triangular and square LC honeycombs
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A series of X-shaped 5,5′-bis(phenylethynyl)-2,2′-bithiophene-based bolaamphiphiles bearing two long lateral alkyl chains and two terminal glycerol groups has been synthesized by using Kumada and Sonogashira coupling reactions as key steps. The thermotropic liquid crystalline behavior of these compounds was investigated by POM, DSC and X-ray scattering. With elongation of the lateral alkyl chains two different kinds of liquid crystalline phases with honeycomb structures, ColhexΔ/p6mm, formed by (defective) triangular honeycomb cells, and Colsqu/p4mm with square cells were observed for these compounds. UV and PL measurements indicate fluorescent properties making them potential candidates for application in fluorescence sensor devices.
- Gao, Hongfei,Cheng, Huifang,Yang, Zonghan,Prehm, Marko,Cheng, Xiaohong,Tschierske, Carsten
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supporting information
p. 1301 - 1308
(2015/02/19)
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- Transition between triangular and square tiling patterns in liquid-crystalline honeycombs formed by tetrathiophene-based bolaamphiphiles
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A series of 5,5′′′-diphenyl tetrathiophenes with polar glycerol groups at each end and two lateral flexible chains self-assemble into a series of liquid-crystalline honeycombs, formed by the π-conjugated rods which enclose polygonal prismatic cells filled by the lateral chains. With increasing chain length a discontinuous transition from triangular to square honeycombs takes place. At this transition a periodic honeycomb composed of a mixture of square and triangular cells in a ratio 1:2 was formed at low temperature, whereas at higher temperature a hexagonal columnar phase composed of triangular and randomly distributed rhombic cells, a new kind of cybotactic nematic phase, and also a cybotactic isotropic phase, both composed of square honeycomb fragments, represent the intermediate states. This provides an example of a dynamic self-assembled system where, depending on the molecular mobility, the transition between two periodic structures with different symmetry either leads to an increase of complexity, or to a chaotic regime with reduced order.
- Cheng, Xiaohong,Gao, Hongfei,Tan, Xiaoping,Yang, Xueyan,Prehm, Marko,Ebert, Helgard,Tschierske, Carsten
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p. 3317 - 3331
(2013/07/26)
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