A synthetic strategy for the synthesis of chiral tetrahydrocarbazoles (THCAs) has been developed. The strategy relies on two types of 6-exo-trig cyclization of 3-substituted indole substrates. Enantioselective domino Friedel-Crafts-type reactions leading to THCAs can be catalyzed by chiral phosphoric acid derivatives (with up to >99% ee), and the first examples of exocyclic Pictet-Spengler reactions to form THCAs are reported.
Hansen, C. L., Ohm, R. G., Olsen, L. B., Ascic, E., Tanner, D. A., & Nielsen, T. E. (2016). Catalytic Enantioselective Synthesis of Tetrahydocarbazoles and Exocyclic Pictet-Spengler-Type Reactions. ORGANIC LETTERS, 18(23), 5990-5993. https://doi.org/10.1021/acs.orglett.6b02718