Ti-Catalyzed Synthesis of Exocyclic Allenes on Oxygen Heterocycles

A general method for the straightforward synthesis of exocyclic allenes on five-, six-, seven-, and eight-membered oxygen heterocycles is described. A Barbier-type titanocene(III)-catalyzed cyclization of propargyl halides with a pendant carb-onyl group is the key step of the process. This reaction is compatible with many functional groups, and can be smoothly carried out under neutral and mild conditions at room temperature.