Iron-Catalyzed Dehydrogenative [4 + 2] Cycloaddition of Tertiary Anilines and Enamides for the Synthesis of Tetrahydroquinolines with Amido-Substituted Quaternary Carbon Centers

An iron-catalyzed dehydrogenative [4 + 2] cycloaddition reaction of tertiary anilines and enamides for the synthesis of tetrahydroquinolines with amido-substituted quaternary carbon centers has been developed. The reaction proceeds through iron-catalyzed dehydrogenation of tertiary anilines followed by nucleophilic addition/intramolecular cyclization with enamides to afford tetrahydroquinolines with amido-substituted quaternary carbon centers in good yields. The reaction tolerates a wide range of functional groups and proceeds under mild conditions. The mechanism for the dehydrogenative [4 + 2] cycloaddition has been confirmed by DFT calculations.