Transforming electron-rich hetero-buckybowls into electron-deficient polycycles

Abstract

Hetero-buckybowl trichalcogenasumanenes (TCSs, 1/2) are electron rich and feature oxidative reactions. Herein, the compounds 1/2 are selectively oxidized by nitric oxide species to afford diverse products. In the presence of tert-butyl nitrite (condition a), two flanking benzene rings on trithia-(1)/triselena-(2) sumanene are oxidized to give 3/4, where one ring is opened and the other is converted to ortho-quinone. When NaNO₂-TFA is the oxidant (condition b), compounds 1/2 are transformed into 5/6 with one flanking benzene opened while the other two flanking benzenes are oxidized to ortho-quinones. It is found that the butoxy groups on the diimide species 7/8 derived from 1/2 are transformed into ortho-quinones to give 9/10 under condition b. Taking these reactions as a key step, various electron-deficient polycycles, 16–21, which possess imide and pyrazine moieties, are created. Compounds 3–6 and 9/10 show electrochromism due to the existence of the ortho-quinone moiety. The LUMO energies of compounds 18–21 are comparable to the n-type organic semiconductor perylene diimide, and compounds 18–21 can serve as electron acceptors to form complexes with electron-rich polycyles.