Transition Metal Catalyzed Enyne Metathesis.

Enyne metathesis is unique and interesting in synthetic organic chemistry. The reaction is catalyzed by various transition metals such as Cr, Mo, W, Ru, Pd, and Pt. There are two types for enyne metathesis one is caused by [2+2] cycloaddition of a multiple bond and transition metal carbene complex, and the other is an oxidative cyclization reaction caused by low-valent transition metals. In usually, this reaction is used as intramolecular enyne metathesis because it is difficult to control intermolecular enyne metathesis. Intramolecular enyne metathesis is designated as an alkylidene migration reaction since an alkylidene part of alkene migrates to an alkyne carbon. Many cyclic compounds having the diene moiety, which are very useful in organic synthesis, were synthesized using this method. Recently, intermolecular enyne metathesis has been developed between an alkyne and ethylene as novel diene synthesis.