Pd/C-Cu in coupling-cyclization process: a general synthesis of 2-substituted 6-oxopyrrolo[3,2,1-ij]quinoline derivatives

A general and practical synthesis of 2-substituted 6-oxopyrrolo[3,2,1-ij]quinolines has been achieved following a single-step Pd/C-mediated coupling-cyclization strategy. The methodology involves the reaction of 8-iodo-4-oxo-1,4-dihydro quinoline-3-carboxylic acid ethyl ester with a variety of terminal alkynes in the presence of 10% Pd/C-PPh3-CuI as a catalyst system in EtOH. The reaction mechanism and utility of the methodology have been discussed.