This work focuses on biobased reactive diluents' synthesis, continuing with optimized oil-based resin precursor production. Our approach introduces vanillin methacrylate (VanMMA), cinnamyl methacrylate (CinMMA), and vanillyl dimethacrylate (VanDiMMA) synthesis using methacrylic anhydride. The introduced approach involves an innovative and available catalyst, potassium acetate, which possesses much suitable potential compared with the usually used 4-dimethylaminopyridine (DMAP). Moreover, we separated the formed secondary product, methacrylic acid (MA), and used it to modify rapeseed oil to prepare a curable thermoset. All synthesized products were structurally verified via complex cross-analysis (NMR, ESI-MS, and FTIR). The reactive systems were mixed to form a multicomponent mixture appropriate for stereolithography (SLA) and 3D printing. It was found that VanDiMMA exhibited comparable diluting properties to the commercially available and used compound, isobornyl methacrylate (IBOMA), while achieving better mechanical, thermo-mechanical, and thermal properties than IBOMA. VanDiMMA-containing SLA resin reached a tensile strength of 12.7 ± 0.3 MPa, a flexural strength of 16.8 ± 0.4 MPa, a storage modulus of 570 MPa at 30 °C, a glass-transition temperature of 83.7 °C, and the heat-resistant index of 169.5 °C.