1,3-Diphenylbenzo[c]furan dianion: nuclear magnetic resonance characterization of a 4nπ heterocyclic dianion containing oxygen

Abstract

The metal reduction of 1,3-diphenylbenzo[c]furan (1) to the corresponding dianion (1^2–) has been carried out by alkali-metal. A detailed (1D and 2D) n.m.r. investigation of (1^2–) enables characterization of its charge distribution as well as its spatial structure. The spectra of (1^2–) differs when three alkali-metals are used for the reduction process. These differences are explained by an ion-solvation equilibrium which in turn explains the different stereoselectivity observed in the quenching experiments of the salts of (1^2–). The reduction process induces in (1^2–) a very high energy barrier for the rotation of the phenyl substituents.