Platinum(II)-Catalyzed Cyclizations Forming Quaternary Carbon Centers, Using Enesulfonamides, Enecarbamates, or Enamides as Nucleophiles

Cyclic enesulfonamides, enecarbamates, or enamides tethered to an alkyne cyclize readily with use of platinum(II) chloride. This reaction generates quaternary-substituted carbon centers within simple spiro-fused or more complex tri- and tetracyclic heterocyclic ring systems. The yields for this process range from 50% to 83%. [reaction: see text].