Synthesis,Structures, and Properties of Highly Strained Cyclophenylene–Ethynylenes with Axial and Helical Chirality |
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| Authors: | Li-Hsiang Wang Norihiko Hayase Dr Haruki Sugiyama Juntaro Nogami Prof Dr Hidehiro Uekusa Prof Dr Ken Tanaka |
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| Institution: | 1. Department of Chemical Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo, 152-8550 Japan;2. Research and Education Center for Natural Sciences, Keio University, Hiyoshi 4-1-1, Kohoku, Yokohama, Japan;3. Department of Chemistry, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo, 152-8550 Japan |
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| Abstract: | Single and double cyclophenylene–ethynylenes (CPEs) with axial and helical chirality have been synthesized by the Sonogashira cross-coupling of di- and tetraethynyl biphenyls with a U-shaped prearomatic diiodoparaphenylene followed by reductive aromatization. X-ray crystallographic analyses and DFT calculations revealed that the CPEs possess highly twisted bent structures. Bend angles on the edge of the paraphenylene units were close to the value of 5]cycloparaphenylene (CPP)—the smallest CPP to date. The double and single CPEs possessed stable chirality despite flexible biphenyl structures because of the high strain in the diethynyl–paraphenylene moiety. In both the single and double CPEs, orbital interactions along the biphenyl axis were observed by DFT calculations in LUMO and LUMO+2 of the single CPE and LUMO+1 of the double CPE, which likely cause lowering of these orbital energies. Concerning chiroptical properties: boosting of the gabs value was observed in the biphenyl-based double CPE, as well as the binaphthyl-based single CPE, compared to the biphenyl-based single CPE. |
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| Keywords: | alkynes axial chirality biaryls cyclophenylene–ethynylenes helical chirality |
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