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 <i>Echinochloa crusgalli</i> were evaluated. Biological assays demonstrated that compounds <b>3h</b>, <b>3af</b>, <b>3ag</b>, <b>3aj</b>, and <b>3bc</b> 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 <b>3af</b> showed excellent pre-emergence herbicidal activity against <i>E. crusgalli</i> 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, <b>3af</b> exhibited good post-emergence herbicidal activity against <i>E. crusgalli</i> 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 <b>3af</b> and <b>3ag</b> with dual functions inhibited the growth of weeds and promoted the growth of radish, <i>Solanum lycopersicum</i>, asparagus lettuce, and soybean, which had great potential for future applications.