Study On Synthesis And Herbicidal Activity Of Pyrazole Ethers Derivatives

Photosynthetic pigments inhibitors with chlorophylls and carotenoids as the site of action ensure the selectivity between plants and animals and become a research focus in developing new herbicides due to their ultra-high efficiency and low toxicity. By the introduction of benzothiazole/benzoxazole/pyrimidine moieties into pyrazole ring and fluoric group/phenyl group substituted at the 1-position on pyrazole ring, 22 new pyrazole ethers compounds were designed and synthesized. The biological activities of 22 pyrazole ethers derivatives were evaluated against Brassica campestris L., Amaranthus retroflexus L., Portulaca oleracea L., Pennisetum alopecuroides L., Echinochloa crus-galli L. and Digitaria sanguinalis L. respectively.1. The synthesis of pyrazole ethers derivatives:The intermediates 3-methyl-1-(2,2,2-trifluoroethyl)-5-pyrazolone and 3-methyl-1-phenyl-5-pyrazolone were obtained by the reaction of 2,2,2-trifluoroethyl hydrazine or benzene hydrazine with ethyl acetoacetate, these intermediates in alkaline DMSO solvent reacted with heterocyclic compounds to obtain target products of pyrazole ethers derivatives. The structures of all new target compounds were confirmed by Elementary analysis, 1H NMR, 13 C NMR and LC-MS.2. The determination of biological activity of pyrazole ethers derivatives:1) All compounds have been tested the inhibition of the shoots and roots growth of Brassica campestris L., Amaranthus retroflexus L., Portulaca oleracea L., Pennisetum alopecuroides L., Echinochloa crus-galli L. and Digitaria sanguinalis L in the concentration of 10 mg/L and 100 mg/L, the compounds 3a, 3b, 3d, 4a, 4b, 4d showed good herbicidal activity among them.2) Further screening in greenhouse conditions, the compound 3d showed 82% post-emergence herbicidal effect against Digitaria sanguinalis L. at the dosage of 750 g/ha and also showed good bleaching activity to Digitaria sanguinalis L. Compound 3d inhibited the synthesis of chlorophyll, and showed the same inhibition activity as commercial standard diflufenican against Brassica campestris L. Gramineous weed Pennisetum alopecuroides L., Echinochloa crus-galli L. and Digitaria sanguinalis L. were slightly sensitive to diflufenican than compound 3d.3) 2,2,2- trifluoroethyl substituted at the 1-position on pyrazole played important role in hebicidal activities of pyrazole ethers derivatives. The electron-withdrawing bromine group at C-4 had no beneficial effect on activity. The pyramidine substituted at the 5-position on pyrazole played more important role in inhibition than that of compounds substituted with benzoheterocycle group.