External Reductant-free Stepwise [3+2] Cycloaddition/Reductive Cyclization from 2-Nitrochalcones and Isocyanides: Synthesis of Pyrrolo[3,4-c]quinolineN-oxides

A novel and unprecedented route for the synthesis of pyrrolo[3,4-c]quinolineN-oxides is described. The synthetic approach involves a stepwise [3+2] cycloaddition/reductive cyclization from readily available 2-nitrochalcones and activated methylene isocyanides. The unique feature of this transformation is the reductive cyclization of C-N bond forming without any external reductants. Moreover, the application of pyrrolo[3,4-c]quinolineN-oxides is realized to formed pyrrolo[3,4-c]quinoline derivatives.