Design,Synthesis,and Herbicidal Activity Of Triketones And Pyrazoles Containing A Pyrimidine Fragment

The issue of food security is the focus of attention of all countries in the world,and weeds are a major factor that endangering food security.Herbicides are the most effective way to control weeds,but with the long-term,single and large-area use of herbicides,the selectivity of herbicides is poor and weed resistance have become increasingly serious.Therefore,the development of new,efficient and environmentally friendly herbicides is the inevitable trend of pesticide development,which is not only the key to ensure the sustainable development of modern agriculture,but also an important aspect to guarantee food quality and safety.Triketone and pyrazole herbicides are two important HPPD enzyme inhibitors,which have the characteristics of high activity,low toxicity,strong selectivity and environmental friendliness,and have received widespread attention.The common structure of these two herbicides is that they both contain 2-benzoyl ethylene-1-ol group.Therefore,in this paper,two series of 42 target compounds,pyrimidine triketones and pyrimidine pyrazole,were designed and synthesized by introducing pyrimidine groups for structural derivation on the basis of retaining the structural fragments of 2-benzoyl ethylene-1-ol.Based on their structure characterization,their herbicidal activities were tested.The specific contents are as follows:PartⅠ:Synthesis and herbicidal activity of triketone compounds containing pyrimidine structureTen key intermediates,pyrimidine oxybenzoic acid derivatives（M-1～M-10）,were prepared from（un）substituted methyl salicylate and 4,6-dimethoxy-2-pyri midine sulfonate by nucleophilic substitution reaction,alkaline hydrolysis and a cidification.Their structures were characterized by ¹H NMR,¹³C NMR and ele mental analysis.It reacts with oxalyl chloride to produce the corresponding acy l chloride,and then condenses with 1,3-dicarbonyl compound to form enol este r,finally undergoes a rearrangement reaction under the catalysis of trimethylsily l cyanide to obtain 22 target compounds-containing pyrimidine structure Triketo ne derivatives（TM-1～TM-22）.Their structures were confirmed by ¹H NMR,¹³C NMR and elemental analysis.Preliminary herbicidal activities of target compounds were tested by glasshouse tests.The results showed that some of the target compounds showed good herbicidal activities against dicotyledonous plant Brassica campestris and amaranth,and the monocotyledon barnyardgrass and crabgrass at 50 g/mu,and the control effect on the dicotyledonous plant amaranth was particularly outstanding.For example,the inhibition rates of compounds TM-1,TM-4,TM-7,TM-11,TM-17,TM-21 and TM-22 against amaranth were more than 80%.Among them,the inhibition rates of compounds TM-11 against amaranth were 99.6%and 100%,which were equivalent to the commercial herbicide acetochlor and mesotrione（16.7 g/mu）.Regardless of post-emergence treatment or Pre-emergence treatment,some compounds have better control effects on rape than acetochlor;In post-emergence treatment,most compounds had better control effect on amaranth than commercial herbicide acetochlor.Even at the dose of 12.5 g/mu,in Pre-emergence treatment,the inhibitory rate of compound TM-17 against amaranth were 94.4%,which is worthy of further research.In addition,the structure and herbicidal activity of the compounds also showed a certain relationship:the introduction of the substituent R¹ on the benzene ring of the target compound is not good for the herbicidal activity,and the introduction of two methyl groups at the 5-position（R²）of cyclohexenone also decreased the herbicidal activity.But when R¹=H and R²=CH₃,the control effect of compound TM-11 on amaranth was better than TM-1（R¹=R²=H）.When cyclohexene ketone was partially replaced by cyclopentenone,regardless of post-emergence treatment or Pre-emergence treatment,compounds TM-21 and TM-22 had strong inhibitory effect on amaranth（>90%）,and their control effect on rope was obviously improved.These results laid the foundation for our further work.PartⅡ:Synthesis and herbicidal activity of Pyrazole compounds containing pyrimidine structureTwenty novel pyrazole compounds（TM-23～TM-42）containing pyrimidine structure were synthesized by the reaction of pyrimidine oxobenzoic acid（M-1～M-10）with acyl chloride,and then reacted with pyrazolone to form corresponding enol esters,and after the rearrangement reaction.The structures of all the target compounds were confirmed by ¹H NMR,¹³C NMR and elemental analysis.The preliminary herbicidal activities of the target compounds（TM-23～TM-42）were tested by rape cup test and barnyardgrass cup test.The results showed that some of the target compounds showed good herbicidal activity against dicotyledonous rape and monocotyledonous barnyardgrass,and the effect on rape was better.For example,the inhibition rate of the compound TM-29 on rape root is 79.6%and 87.3%at 10 and100μg/m L,respectively.The preliminary structure-activity relationship showed that the change of R¹ position in benzene ring of target compounds had an important effect on the inhibition effect of rape root,but the change of R² on pyrazole ring had little effect on the herbicidal activity;for barnyardgrass,the introduction of R¹on benzene ring was detrimental to the herbicidal activity.These results provide a basis for the further design of highly active compounds.