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 beta-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(sp(3))-H functionalization adjacent to carbonyl group on the beta-alkynyl ketone unit.