Efficient syntheses of π-electron deficient macrocycles

ABSTRACT

Cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺) cyclophane represents an ideal π-electron deficient macrocycles, which demonstrates the extraordinary ability of hosting a variety of π-electron-rich guests in its rigid, preorganised cavity. However, this macrocycle undergoes large ring strain and therefore its preparation is often low yielding. In order to increase its yields, high-dilution conditions and template-directed synthesis are employed, which are rather time-consuming, i.e. a few weeks including template removal. Herein, we attempt to solve these problems by either using click reaction, or decreasing the ring strain by using a flexible linker. Three analogues of CBPQT⁴⁺ ring were synthesised without the need of guest template, each of which contains two bipyridinium units. Two of these three macrocycles are able to recognise π-electron rich guests within their cavities. However, the one obtained via click reaction demonstrates low guest recognition ability.

Graphical Abstract

KEYWORDS:

• Host–guest recognition
• click reaction
• macrocyclisation
• π-electron interactions

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

Support from the Chinese “Thousand Youth Talents Plan”, the National Natural Science Foundation of China [No. 21772173, 91856116 and 21922108], and the Natural Science Foundation of Zhejiang Province of China [No. LR18B020001], as well as “the Fundamental Research Funds for the Central Universities” [No. 2019FZA3007] are gratefully acknowledged.