A RU CATALYZED ADDITION OF ALKENES TO ALKYNES

The potential of the Alder ene reaction which possesses high atom econ omy is not realized because of limitations of scope and selectivity. T hus, the thermal bimolecular addition of unactivated alkenes to unacti vated alkynes has not been reported. This addition now becomes possibl e through the advent of ruthenium catalysis. Several ruthenium complex es are effective including (PhOCH(3))(Ph(3)P)RuCl2, (p-cymene)(Ph(3)P) RuCl2, (p-cymene)[(C4H9)(3)P]RuCl2, and CpRu(COD)Cl, but the latter gi ves the highest conversions and regioselectivities. The reaction best proceeds in aqueous DMF at 100 degrees C or methanol at reflux. Both i nternal and terminal alkynes react. Monosubstituted alkenes are requir ed. The reaction exhibits extraordinary chemoselectivity and control o f product double bond geometry. A mechanism envisioning formation of a ruthenacyclopentene accounts for the experimental observations.