Domino Palladium-Catalyzed Double Norbornene Insertion/Annulation Reaction: Expeditious Synthesis of Overcrowded Tetrasubstituted Olefins.

A Pd-catalyzed domino process involving a double norbornene insertion/annulation reaction was developed for the expeditious synthesis of overcrowded olefins. In this one-pot reaction, four new C-C bond formations were achieved by three consecutive Heck carbopalladations and C-H activation across the C≡C triple bond of 2-alkynyl bromobenzenes with two norbornene rings via a reactive vinylic-Pd(II) species. This protocol provides a step-economical synthetic system to access the structurally identical molecular machine motifs of overcrowded olefins with high yields.