Halogen Bond-Catalyzed Friedel–Crafts Reactions of Aldehydes and Ketones Using a Bidentate Halogen Bond Donor Catalyst: Synthesis of Symmetrical Bis(indolyl)methanes

The use of a halogen bond donor to catalyze Friedel–Crafts reactions of indoles with a range of aldehydes and ketones to directly produce bis­(indolyl)­methanes, including the natural products arsindoline A, arundine, trisindoline, and vibrindole A, is reported. The bidentate catalyst used in these reactions proved to be more effective than a monondentate analogue, a thiourea commonly used as an organocatalyst, and even a trityl cation that has been used previously in the synthesis of bis­(indolyl)­methanes.