Construction of Bridged Carbocycles and Heterocycles via Rh(III)-Catalyzed C–H Alkylation/Michael Addition of 2‑Arylindoles with Quinone Monoacetals

A rhodium-catalyzed
formal [4 + 5] annulation reaction of 2-arylindoles
with quinone monoacetals for the selective preparation of bridged
nine-membered carbocyclic and heterocyclic compounds is developed.
When 2-aryl substituted indoles are employed, this annulation reaction
affords bridged nine-membered carbocyclic compounds with excellent
indolyl C3 selectivity. On the other hand, with 2-aryl-3-substituted
indoles as the substrates, bridged nine-membered heterocyclic compounds
are exclusively formed via N1 annulation. Further transformations
of the obtained products into new bridged compounds showcase the synthetic
potential of this protocol.