Synthesis and herbicidal activity against barnyard grass of novel diarylmethanone O ‐(2,6‐bis((4,6‐dimethoxypyrimidin‐2‐yl)oxy)benzoyl)oximes

BACKGROUND: Pyribenzoxim is an excellent herbicide that can effectively control barnyard grass. However, there are few reports of its structural analogs and structure-activity relationship (SAR), which makes pyribenzoxim an isolated case. Here, a series of diarylmethanone oxime esters characterized by pyridine heterocycles were designed and synthesized for herbicidal screening and SAR investigation against barnyard grass. RESULTS: At greenhouse treatment concentrations of 1.17-37.5 mug mL(-1) , the title compounds showed a positive dose-toxicity correlation toward barnyard grass plants, with the damage becoming progressively more serious over time. At a concentration of 18.75 mug mL(-1) and above, obvious damage was observed in 3 days, most plants died in 7 days, and all died in 14 days. Different degrees of damage were also seen when the concentration was lower than 9.38 mug mL(-1) . The selected compounds 5-20 and 5-21 showed excellent control against Echinochloa crusgalli (L.) Beauv., Leptochloa chinensis (L.) Nees, Cyperus difformis L. and Lindernia procumbens (Krock.) Philcox in paddy fields, which was slightly better than that of pyribenzoxim. CONCLUSION: SAR analysis of greenhouse data revealed that the type and position of substituents on aromatic rings greatly influenced the activity of the compounds, although log P values showed no obvious correlation with activity. Combined with compounds 5-20 and 5-21, which showed moderate and excellent activity in greenhouse experiments, and excellent activity in controlling barnyard grass in the field, we conclude that pyribenzoxim analogs probably act as prodrugs, and this could be a focus of attention in future studies on structural optimization of the herbicide. (c) 2020 Society of Chemical Industry.