Stable Bromiranium Ion Salts as Reagents for Biomimetic Indole Terpenoid Cyclizations.

Indole terpene alkaloids are a diverse group of natural products and show significant biological activities. To enable their biomimetic synthesis, electrophilic bromocyclization of polyenyl indole derivatives could be achieved using sterically demanding bromiranium ion salts with the weakly coordinating counterion BArF- as reagent. Starting from polyenyl indole derivatives, the corresponding bromocyclization products have been obtained with very high diastereoselectivity and in good yields.