Gold-Catalyzed Cascade Reactions of 4H‑Furo[3,2‑b]indoles with Allenamides: Synthesis of Indolin-3-one Derivatives

Merging the ability of cationic gold­(I) catalysts to activate unsaturated π-systems with the electrophiles-driven ring-opening reactions of furans, we describe a new approach to synthesize 2-spiroindolin-3-ones from 4H-furo­[3,2-b]­indoles. The reaction occurs through a cascade sequence involving addition of a gold-activated allene to the furan moiety of the starting furoindole followed by a ring-opening/ring-closing event affording 2-spirocyclopentane-1,2-dihydro-3H-indolin-3-ones in moderate to good yields.