Silver/Scandium-Cocatalyzed Bicyclization of β‑Alkynyl Ketones Leading to Benzo[c]xanthenes and Naphtho[1,2‑b]benzofurans

The combination of AgTFA and Sc­(OTf)3 enables the bimetallic synergistic catalysis of β-alkynyl ketones and para-quinone methides (p-QMs), allowing direct synthesis of 17 examples of benzo­[c]­xanthenes with generally good yields through a benzannulation/1,6-addition/cyclization sequence. Exchanging p-QMs for quinone imine ketal resulted in 10 examples of tetracyclic naphtho­[1,2-b]­benzofurans via a similar benzannulation/1,4-addition/cyclization cascade. During these reaction processes, AgTFA and Sc­(OTf)3 could be perfectly compatible, together with the realization of C­(sp3)-H functionalization adjacent to carbonyl group on the β-alkynyl ketone unit.