Synthesis of Flake-shaped [3]Cyclo-4,6-dibenzofuranylene

Abstract

The cyclic trimer of dibenzofuran linked at the 4,6-positions, named [3]cyclo-4,6-dibenzofuranylene, was synthesized by Ni(0)-mediated reductive coupling of 4,6-dibromodibenzofuran. DFT calculation indicated that the flake-shaped C2 symmetric structure is the most stable conformer and the propeller-shaped D3 symmetric structure is the minor conformer with a higher energy (+19.1 kcal mol−1). The calculated inversion energy of the C2 conformer through a Cs symmetric transition state was +4.1 kcal mol−1, showing rapid fluctuation, which is consistent with the observation of only one set of 1H NMR signals of dibenzofuran of [3]cyclo-4,6-dibenzofuranylene.