Palladium-Catalyzed Sonogashira-Coupling Conjoined C-H Activation: A Regioselective Tandem Strategy to Access Indolo- and Pyrrolo[1,2-a]quinolines

An operationally simple approach for the regioselective tandem synthesis of indolo[1,2-a]quinolines 4a-v and pyrrolo[1,2-a]quinolines 5a-k from 1-(2-bromophenyl)-1H-indole/pyrrole/imidazole 1a-c, 2a,b by the palladium-catalyzed sequential C-C bond formation is described. The developed approach involves the palladium-catalyzed Sonogashira coupling followed by the intramolecular C-C bond formation via C-H activation, which leads to the formation of 6-endo-dig cyclized product. This synthetic methodology accommodates wide functional group variation on alkyne, which proves to be advantageous for the structural and biological activity assessments.