A simple protocol for the transesterification of highly unsaturated vegetable oils such as calendula oil and tung oil, catalyzed by sodium methoxide, is described. Calendula oil contained about 59–65% of calendic acid (8,10-trans,12-cis-octadecatrienoic acid) (1a), and tung oil about 84% of α-eleostearic acid (9-cis,11,13-trans-octadecatrienoic acid) (2a). Transesterifications of calendula oil with alcohols such as methanol, ethanol, and isopropanol give the respective calendula oil esters, which were tested as reactive diluents for alkyd resins in coating formulations. Especially ethyl and isopropyl calendula oil esters showed good properties, including low viscosity and good drying performance. Furthermore, a shortening of the drying time of about 35–40% compared to conventionally prepared formulations was achieved. Analogously, the respective esters of tung oil were synthesized and used as reactive diluent.