A method for modifying ethylenic unsaturation in a triglyceride. One or more unsaturated fatty acyl moieties present in the triglyceride are substituted with a a lactone substitution, a dihydrofuran substitution, or a ketone substitution via an electron acceptor mediated reaction. The resulting reaction products are useful, for example, as lubricants, metalworking fluids, mold release agents, hydraulic fluids, or dielectric fluids, or as components of lubricants, metalworking fluids, mold release agents, hydraulic fluids, or dielectric fluids, and modified fatty acids for polymer synthesis.