Total Synthesis of Naturally Occurring Pyrano[3,2-a]carbazoles via a Unified Copper-Catalyzed Cascade Strategy.

We report a copper-catalyzed cascade for the synthesis of pyrano[3,2-a]carbazole natural products. This strategy employs C3-substituted indolyl α-diazocarbonyl compounds to construct the pyrano[3,2-a]carbazole framework through sequential C-C and C-O bond formation in a single transformation. The approach cumulated in the synthesis of seven natural products, including the first total synthesis of clausenanisine B. Preliminary antimicrobial screening identified a concentration-dependent activity against fungi and Gram-positive bacteria for select members of the synthesized library.