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

Ke Chen,¹ Shuai Liu,¹ Dan Wang, Wen-Juan Hao,* Peng Zhou, Shu-Jiang Tu,* and Bo Jiang*

（¹These authors contributed equally to this work）

The combination of AgTFA and Sc(OTf)₃ enables the bimetallic synergistic catalysis of b-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 (QIK) 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.

J. Org. Chem.2017, DOI:10.1021/acs.joc.7b02134