Ligand-free Cu-catalyzed [3 + 2] cyclization for the synthesis of pyrrolo[1,2-a] quinolines with ambient air as a terminal oxidant

A ligand-free Cu-catalyzed [3 + 2] cycloaddition of ethyl 2-(quinolin-2-yl)acetates, ethyl 2-(isoquinolin-1-yl)acetates, and ethyl 2-(pyridin-2-yl)acetates with (E)-chalcones for a "one-pot" synthesis of pyrrolo[1,2-a]quinolines, pyrrolo[2,1-a]isoquinolines and indolizines has been developed. The annulation products were isolated in moderate to good yields with air as the sole oxidant under mild conditions.