Synthesis, Structures, and Properties of Highly Strained Cyclophenylene–Ethynylenes with Axial and Helical Chirality. Issue 41 (18th August 2020)

• Record Type: Journal Article
• Authors: Wang, Li‐Hsiang; Hayase, Norihiko; Sugiyama, Haruki; Nogami, Juntaro; Uekusa, Hidehiro; Tanaka, Ken
• Is Part Of: Angewandte Chemie international edition. Volume 59:Issue 41(2020)
• Page Start: 17951
• Page End: 17957
• Publication Date: 2020-08-18
• Subjects: alkynes -- axial chirality -- biaryls -- cyclophenylene–ethynylenes -- helical chirality; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202006959
• Languages: English
• ISSNs: 1433-7851

Abstract

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 g abs value was observed in the biphenyl‐based double CPE, as well as the binaphthyl‐based single CPE, compared to the biphenyl‐based single CPE. Abstract : Single and double cyclophenylene–ethynylenes (CPEs) with stable axial and helical chirality have been synthesized, which possess highly twisted bent structures and interesting chiroptical properties. Orbital interactions are observed along the biphenyl axis in both the single and double CPEs. Boosting of the g abs value occurs in the biphenyl‐based double CPE and in the binaphthyl‐based single CPE, in contrast with the biphenyl‐based single CPE.