Ruthenium Catalyst Dichotomy: Selective Catalytic Diene Cycloisomerization or Metathesis

Ruthenium based catalysts are versatile promoters of a large variety of reactions. A catalytic system active in metathesis has been generated in situ from [RuCl2(p-cymene)]2, 1,3-bismesitylimidazolinium chloride, as precursor of a bulky carbene ligand, and cesium carbonate. We report that this three component catalytic system exhibits dichotomous reactivity for the transformation of dienes, providing an active catalytic system for the cycloisomerization of dienes to methylidene five-membered cyclic molecules, whereas, in the presence of acetylene, a metathesis catalyst is generated that transforms the same dienes into cyclic olefins with loss of ethylene.