We have been interested in the application of catalytic reactions for the synthesis of potential pharmaceuticals.^[1] For the development of new kinase inhibitors, we prepared a small compound library of unsymmetrical bisindoles. Annulated Hymenialdisine-type bisindoles can be obtained via a solvent-free and efficient C-C bond-formation reaction on silica under mild conditions from a hydroxyl precursor (±)-1 or aziridines (±)-3.^[2]

Surprisingly, both nitrogen atoms of (±)-3 were deprotected in situ yielding products (±)-4 directly. These reactions enable easy manageable and fast diversification pathways for a number of unsymmetrical bisindoles and pharmaceutically interesting Hymenialdisine derivatives.

^[1]Kumar, K.; Michalik, D.; Castro, I. G.; Tillack, A.; Zapf, A.; Arlt, M.; Heinrich, T.; Böttcher, H.; Beller, M. Chem. Eur. J. 2004, 10, 746-757. ^[2]Kaiser, H. M.; Lo, W. F.; Riahi, A. M.; Spannenberg, A.; Beller, M.; Tse, M. K. Org. Lett. 2006, 8, 5761-5764.