Ruthenium(II)-Catalyzed [2 + 2 + 2] Cycloaddition of 1,6-Diynes with Tricarbonyl Compounds

In the presence of catalytic amounts of Cp*Ru(cod)Cl, unsymmetrical 1,6-diynes possessing a variety of functional groups reacted with electron-deficient tricarbonyl compounds at the ketone CO double bonds to selectively afford dienones via electrocyclic ring opening of the expected α-pyrans. The intramolecular Michael addition of the cycloadducts having an acetyl and an alkylidenemalonate moiety gave bicyclo[3.3.0]octenone derivatives.