One-Pot Synthesis of Dihydrobenzo[a]fluorenes via Cascade C-H Annulation of Thiobenzamide with Alkynes.

We herein disclose a highly efficient one-pot synthetic strategy for dihydrobenzo[a]fluorenes via cascade rhodium(III)-catalyzed ortho-C-H activation/annulation of thiobenzamides with aryl ethynyl ketones and subsequently copper(II)-promoted intramolecular C-H/C-H cross-coupling reactions. Mechanistic investigations suggest that Cu(II) plays two crucial roles by serving as a sulfide scavenger to regenerate the Rh(III) catalyst and promoting the intramolecular C-H/C-H cross-coupling reaction. This protocol greatly streamlines accesses to a variety of appealing tetracyclic benzo[a]fluorene skeletons, which may have potential biological activity and medicinal properties.