Sixfold Peripheral Halogenation of Tribenzotriquinacenes: An Alternative Access to Useful TBTQ Building Blocks

Abstract

Sixfold electrophilic bromination and iodination of the molecular periphery of the bridgehead-tetramethylated tribenzotriquinac­ene (TBTQ) with N-bromosuccinimide (NBS) and N-iodosuccinimide (NIS), respectively, under various conditions was studied to develop an alternative preparative approach to the classical Lewis acid catalyzed bromination. Running these reactions in trifluoroacetic acid either in pure form or with chloroform as a co-solvent at elevated temperatures, or under sonication or microwave irradiation was found to give increasingly fast and efficient conversion of TBTQ to the target hexahalogenated TBTQ derivatives in excellent yields. NIS was found to be markedly more reactive than NBS, whereas N-chlorosuccimide reacted hardly. The new method was applied to the sixfold functionalization of the 4b,8b,12b-tripropyl-12d-methyl-TBTQ analogue to give the corresponding hexabromo and hexaiodo derivatives. Some sixfold C–C cross-coupling reactions of hexahalo derivatives of TBTQ were carried out in excellent yields to enlarge the three spatially orthogonal indane wings of the TBTQ core.