Synthesis of novel 2,8-disubstituted indolo[3,2-b]carbazoles

A new synthetic pathway towards 2,8-difunctionalised indolo[3,2-b]carbazoles was investigated. The presented method offers a short and high yielding route towards 2,8-dibromo-5,11-dihexyl-6,12-diphenyl-indolo[3,2-b]carbazole. It is demonstrated that the latter compound is a versatile building block, enabling the synthesis of a number of previously unreported 5,11-dialkyl-6,12-diphenyl-indolo[3,2-b] carbazoles in moderate to good yields, using Suzuki and Sonogashira cross-coupling reaction. Furthermore it is shown that 2,8-dibromo-5,11-dihexyl-6,12-diphenyl-indolo[3,2-b] carbazole can be easily formylated, giving rise to the 2,8-diformyl-5,11-dihexyl-6,12-diphenyl-indolo[3,2-b] carbazole. The latter compound was successfully subjected to condensation reactions.