NHC-Mediated Synthesis of Tricyclic Spirocarbocycles via an Intramolecular Stetter Reaction of Cyclic Enal-Enones.

A general and efficient method for the synthesis of tricyclic spirocarbocycles is described. Various cyclic enal-enones were reacted with an N-heterocyclic carbene, and an intramolecular Stetter reaction proceeded smoothly to give various tricyclic spiro-1,4-diketones in 31-72% yields. The ring size of the spiro compounds can be easily controlled using different cyclic enals and enones or by altering the length of the carbon tether.