Synthesis of fluorenes via tandem copper-catalyzed [3 + 2] cycloaddition and rhodium-catalyzed denitrogenative cyclization in a 5-exo mode from 2-ethynylbiaryls and N-sulfonyl azides in one pot.

An efficient synthetic method of fluorenes having an enamine moiety at C-9 methylene bridge is developed from N-sulfonyl-4-biaryl-1,2,3-triazole derivatives via Rh-catalyzed denitrogenative cyclization in a 5-exo mode. Rh-catalyzed denitrogenative cyclization followed by catalytic hydrogenation produces N-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-exo mode starting from 2-ethynylbiaryls and N-sulfonyl azides in one pot.