Synthesis of Substituted Pyrrolo[2,1-a]isoquinolines by Gold-Catalyzed Domino Cyclization of Alkynyl Iminoesters

A novel gold-catalyzed double cyclization leading to a biologically important pyrroloisoquinoline skeleton was established. The reaction sequence involving 6-exo-dig cyclization of alkynyl iminoester and [3+2] cycloaddition of azomethine ylide proceeded smoothly in the presence of 0.5-1.0 mol% (CyJohnPhos)AuCl/AgOTf at 65 or 80 degrees C. This strategy with (-)-phenylmenthol-derived iminoester enables a generation of chiral azomethine ylide in situ to construct an optically active pyrroloisoquinoline in a highly diastereoselective manner. An alkyne and alkenes with electron-withdrawing group could be utilized as dipolarophiles. Iminoesters having terminal and internal alkynes were applied as reaction substrates to afford the corresponding pyrroloisoquinolines.