In(ONf)3-catalyzed 7-membered carbon-ring-forming annulation of heteroarylindoles with α,β-unsaturated carbonyl compounds

A seven-membered carbon-ring-forming annulation occurred, upon treatment of heteroarylindoles with alpha,beta-unsaturated carbonyl compounds in the presence of an indium catalyst. The reductive annulation was observed when octylsilane was used. With 1,3-dibromo-5,5-dimethylhydantoin instead of octylsilane, the oxidative annulation proceeded. These two reactions were completely controlled; this is the first achievement in the biheteroaryl-based seven-membered carbon-ring-forming annulation. Tetracyclic products obtained from the oxidative annulation underwent SEAr-based bromination regioselectively. The resulting Br-C bond was used for the palladium-catalyzed Suzuki-Miyaura cross-coupling reaction to extend the p-conjugated region. Reaction pathways were also discussed based on some mechanistic studies.

Automated summary

A new method for the formation of seven-membered carbon rings in heteroarylindoles reacting with different substrates was discovered in this study, and the two different annulation reactions could be controlled. The resulting tetracyclic products can be further extended through subsequent reactions to expand the p-conjugated region.