Facile Synthesis of Dibenzotetracenedione Derivatives by Rhodium-Catalyzed [2+2+2] Cycloaddition/Spontaneous Aromatization.

Abstract

It has been established that a cationic rhodium(I)/SEGPHOS complex catalyzes the [2+2+2] cycloaddition of biphenyl-linked 1,7-diynes with 1,4-naphthoquinone and anthracene-1,4-dione. Conveniently, spontaneous aromatization proceeded upon removal of the rhodium complex by passing the reaction mixture through an alumina column, to give the corresponding dibenzotetracenediones and dibenzopentacenediones, respectively, in good yields. The obtained dibenzotetracenedione could be readily transformed into the corresponding dibenzotetracene in good yield. This dibenzotetracene showed blue fluorescence with a good quantum yield, which was significantly higher than those of tetracene, tetrabenzotetracene, and hexabenzotetracene.