Synthesis of alfa,beta-Unsaturated 4,5-Disubstituted alfa-Lactones via Ring-Closing Metathesis Catalyzed by the First-Generation Grubbs Catalyst

4-Methyl-5-alkyl-2(5H)-furanones have been prepared by ruthenium-catalyzed ring-closing metathesis of the suitable methallyl acrylates. Despite the electron deficiency of the conjugated double bond and of the gem-disubstitution of the allylic alkene moiety in the starting acrylates, the first-generation Grubbs' catalyst I proved to be an effective promoter for the ring closure, affording the expected butenolides in good to high yields.