Palladium/Norbornene-Catalyzed C?H Alkylation/Alkyne Insertion/Indole Dearomatization Domino Reaction: Assembly of Spiroindolenine-Containing Pentacyclic Frameworks

Article abstract of DOI:10.1002/anie.201801894

Reported is a highly chemoselective intermolecular annulation of indole-based biaryls with bromoalkyl alkynes by using palladium/norbornene (Pd/NBE) cooperative catalysis. This reaction is realized through a sequence of Catellani-type C?H alkylation, alkyne insertion, and indole dearomatization, by forming two C(sp²)?C(sp³) and one C(sp²)?C(sp²) bonds in a single chemical operation, thus providing a diverse range of pentacyclic molecules, containing a spiroindolenine fragment, in good yields with excellent functional-group tolerance. Preliminary mechanistic studies reveal that C?H bond cleavage is likely involved in the rate-determining step, and the indole dearomatization might take place through an olefin coordination/insertion and β-hydride elimination Heck-type pathway.