Design, Synthesis, and Bioactivity of Novel Ethyl 2-Oxo-4-phenylbut-3-enoate Derivatives as Potential Herbicide Candidates

Natural products play a significant role in the development of new ecofriendly herbicides to control weeds. In this study, thirty-seven ethyl 2-oxo-4-phenylbut-3-enoate derivatives featuring an alkyl amine group were rationally designed and facilely synthesized based on a structural splicing strategy from the natural product cinnamic acid. Their vitro and greenhouse herbicidal activities against Echinochloa crusgalli were evaluated. Biological assays demonstrated that compounds 3h, 3af, 3ag, 3aj, and 3bc exhibited excellent herbicidal activities, with root and stem growth inhibition rates exceeding 95.0% at a concentration of 50 μg/mL, which were superior to those of acetochlor. The greenhouse experimental data indicated that compound 3af showed excellent pre-emergence herbicidal activity against E. crusgalli with a fresh-weight inhibition rate of 80.0% at the dosage of 400 g ai/ha, which was better than the frequently used acetochlor. Additionally, 3af exhibited good post-emergence herbicidal activity against E. crusgalli with a fresh-weight inhibition rate of 73.7% at a dose of 400 g ai/ha, which was comparable to that of the commercial product glyphosate. In addition, crop safety results suggested that compounds 3af and 3ag with dual functions inhibited the growth of weeds and promoted the growth of radish, Solanum lycopersicum, asparagus lettuce, and soybean, which had great potential for future applications.