Synthesis of Fluorenes via Tandem Copper-Catalyzed [3 + 2] Cycloaddition and Rhodium-Catalyzed Denitrogenative Cyclization in a 5-<i>Exo</i> Mode from 2‑Ethynylbiaryls and <i>N</i>‑Sulfonyl Azides in One Pot

Abstract

An efficient synthetic method of fluorenes having an enamine moiety at C-9 methylene bridge is developed from <i>N</i>-sulfonyl-4-biaryl-1,2,3-triazole derivatives via Rh-catalyzed denitrogenative cyclization in a 5-<i>exo</i> mode. Rh-catalyzed denitrogenative cyclization followed by catalytic hydrogenation produces <i>N</i>-tosylaminomethyl-substituted fluorenes in one pot. Moreover, fluorenes are synthesized via tandem Cu-catalyzed [3 + 2] cycloaddition and Rh-catalyzed denitrogenative cyclization in a 5-<i>exo</i> mode starting from 2-ethynylbiaryls and <i>N</i>-sulfonyl azides in one pot