A series of substituted acetophenone oxime esters of Pyrithiobac were synthesized as potential herbicides. The structures of the synthesized new compounds were confirmed by 1H NMR, 13C NMR, HRMS, and X‐ray single‐crystal diffraction (XRD). The pre‐emergence and post‐emergence herbicidal activity studies show that 4‐CF3 (6 f), 4‐NO2 (6 i), 4‐NH2 (6 j), 4‐F (6 l), and 2,4‐2OCH3 (6 s) substituted acetophenone oxime esters of Pyrithiobac exhibit better pre‐emergence and post‐emergence herbicidal activities against monocotyledon and dicotyledon weeds than other synthesized new compounds. In pre‐emergence herbicidal activity study, 6 f, 6 i, 6 j, 6 l, and 6 s exhibit similar herbicidal activities against monocotyledon and dicotyledon weeds as compared to Staple (Pyrithiobac‐sodium). In post‐emergence herbicidal activity study, 6 f, 6 i, 6 j, 6 l, and 6 s exhibit similar herbicidal activities against dicotyledon weeds and better herbicidal activities against monocotyledon weeds as compared to Staple. Compounds 6 i and 6 l with high herbicidal activities and similar binding mode with acetolactate synthase as compared to Staple were further subjected to crop safety study. The results show that the safety of compound 6 l to cotton is as good as Staple and better than 6 i. The present work indicates that compound 6 l may serve as a new candidate for potential herbicides.
Chiral C-X (X=N, O, P, B, F, etc.) bond fragments are present in a wide variety of natural and pharmaceutically active molecules. Transition metal-catalyzed asymmetric hydrogenation is one of the most attractive strategies for the synthesis of these chiral compounds. Among the many transition metal catalysts, earth-abundant transition metals (iron, cobalt, nickel, and copper) have been used in asymmetric hydrogenation to replace rare metals (rhodium, ruthenium, iridium and palladium) due to their abundant reserves, low toxicity, and environmental friendliness. At present, this method for the construction of chiral C-X bonds has become a prominent trend in modern organic chemistry. Among them, the development of nickel catalysts has been relatively rapid. Based on this, the article will review the latest research in the preparation of compounds with chiral C-X bonds via nickel-catalyzed asymmetric hydrogenation using hydrogen. It is divided into five sections consisting of the construction of chiral C-N, C-O, C-P, C-B and C-F bonds by nickel-catalyzed asymmetric hydrogenation.
A series of new trifluoromethyl-substituted phenyl alkyl ketoxime esters of Bispyribac were synthesized as potential herbicides. All synthesized compounds were characterized by nuclear magnetic resonance (NMR) spectroscopy and highresolution mass spectrometry (HRMS). Sprout method and foliar spray method were used to study the herbicidal activity of the synthesized compounds. Among all synthesized compounds, compound 3 (4-trifluoromethylphenyl n-butyl ketoxime ester of Bispyribac) exhibits the highest herbicidal activity against Echinochloa crusgalli (L.) Beauv with median effect dose (ED 50 ) of 1.7 μg/mL in pre-emergence herbicidal activity study. The structure-activity relationship analysis indicates that trifluoromethyl substitution on the phenyl group exhibits better activity than methoxy and methyl substitution on the phenyl group. The alkyl chain length also affects the activity significantly and the optimal alkyl chain length is four among the tested compounds. However, the substitution position of trifluoromethyl exhibits very limited influence on the activity. In post-emergence herbicidal activity study, compound 3 (ED 90 69.1056 g/hm 2 ) exhibits better herbicidal activity against Echinochloa crusgalli (L.) Beauv than Pyribenzoxim (ED 90 99.0810 g/hm 2 ). Moreover, compound 3 exhibits better safety to hybrid rice variety II you 084 and rice variety Nanjing 44 than Pyribenzoxim in crop safety study. Compound 3 may serve as a lead compound for future herbicide discovery.
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