Formation of cyclic indenofluorene dimers by BuLi-induced transannular cyclization of dehydrobenzo[14]annulenes

Abstract

To develop new synthetic methods for polycyclic aromatic hydrocarbons, transannular cyclizations of dehydrobenzo[14]annulene ([14]DBA) derivatives having a butadiyne unit were investigated. When butyllithium was used as a nucleophile, tandem transannular cyclization followed by dimerization took place, giving two cyclic indenofluorene dimers which contain a 9,9'-bifluorenylidene unit. Additionally, monomeric transannular cyclization products derived by addition of two or three butyl groups were obtained. The structures of these products and the reaction mechanism will be discussed.