Diiodomethane-Mediated Generation of N-Aryliminium Ions and Subsequent [4+2] Cycloadditions with Olefins

Herein, we report a method for in situ generation of N-aryliminium ions via reactions of N,N-dimethylanilines with diiodomethane. We used the method to prepare tetrahydroquinolines via one-pot three-component reactions between N ,N - dimethylanilines, diiodomethane, and olefins. This transformation involves initial reaction of the aniline with diiodomethane to form an iodomethylammonium salt, which undergoes fragmentation accompanied by elimination of methyl iodide to give an Naryliminium ion, which is trapped by the olefin via [4 + 2] cycloaddition to give the final product. This method for generating Naryliminium ions requires neither a catalyst nor a strong oxidant, suggesting that it can be expected to find broad utility, especially for substrates that are sensitive to Lewis acids, transition metals, or strong oxidants.