Synthesis of Benzo[a]carbazoles through Visible Light-Induced Cycloaromatization

We report herein a synthesis of 5,6-diarylbenzo[a]carbazoles by a sequence of 6 pi-electrocyclization followed by beta-elimination. The highly functionalized 2,3-disubstituted indoles used for this cycloaromatization process are prepared by Pd-catalyzed cyclizative cross-coupling ofortho-alkynylanilines withortho-alkynylbenzamides. The combination of these two reactions allows us to develop a facile synthesis of benzo[a]carbazoles directly from two easily accessible internal alkynes without isolation of the indole intermediates.