Gold/Scandium Bimetallic Catalyzed Formal [5+2]- and [4+2]-Annulations: Access to Tetracyclic Indole Scaffolds

Regiodivergent formal [5+2]- and [4+2]-annulation reactions of indole derivatives with 2-(2-alkynyl)aryl cyclopropane-1,1-diesters (ACPs) have been developed. A series of tetracyclic indole derivatives were delivered in 77% average yield with excellent regioselectiveties enabled by Au(I)/Sc(Ⅲ) bimetallic relay catalysis. A gram-scale reaction and further transformation of the resulting tetracyclic indoles demonstrated the practical utility of this protocol. Moreover, photophysical properties of the obtained multicyclic compounds were also investigated.