Efficient catalytic cyclizations of three and two imine assemblies: direct access to tetrahydroimidazo[1,5-c]imidazol-7-ones and imidazoles.

A cascade cyclization involving union of three imines by an organocatalyst proline is established to afford new fused-tetrahydroimidazo[1,5-c]imidazol-7-ones with excellent regio- and stereoselectivity. Another dehydrogenative cyclization by union of two imines is developed using the Cu(OTf)(2)-Ag(2)O combo catalyst to furnish functionalized imidazoles.