A series of 3 H-pyrazolo[3,4-d][1,2,3]triazin-4-one derivatives were synthesized as candidate herbicides by diazotization of different 5(3)-amino- N-phenyl-1 H-pyrazole-4-carboxamide derivatives prepared by the reaction of substituted 5(3)-amino-pyrazole-4-carbonyl chloride with a substituted aniline. Their structures were identified by (1)H NMR and elemental analyses. The isomers D and E were isolated, and their structures were identified by two-dimensional NMR analyses (heteronuclear single quantum coherence and heteronuclear multiple-bond correlation) and single-crystal X-ray diffraction analysis. The bioassay results showed that some of the title compounds exhibited both excellent herbicidal activity at a dose of 93.75 g/ha and strong inhibition against protoporphyrinogen oxidase activity in vitro. The structure-activity relationship showed that D16 possessed the highest activities both in vivo and in vitro when the N-substituted group of the pyrazole ring was allyl and the N-substituted group of benzooxazinone was propargyl.

A series of 3-phenyl benzo [d] [1,2,3]triazin-4(3H)-one derivatives were synthesized through the condensation of phenol E and alkyl (alkenyl, alkynyl) chlorides (bromides, iodide) or alkyl chloroacetates or N-alkyl chloroacetamides using K 2 CO 3 as the acid acceptor in N,N-dimethylformamide. Phenol E was prepared from starting material, 5-amino-2-chloro-4-fluorophenyl ethyl carbonate, in four steps involving in amidation, reduction, diazotization, and deprotecting-group reaction. The herbicidal activities of the title compounds were tested against two dicotyledonous plants and two monocotyledonous plants, in which some of them exhibited high herbicidal activities against two dicotyledonous plants in preemergence and postemergence treatments. Moreover, when the dosage was decreased to 180 and 90 g/ha, compounds F1, F8, and F9 showed highly selective inhibitory activities against amaranth pigweed, alfalfa, asteraceae, field sowthistle, morning glory, purslane, and velvetleaf in postemergence treatment but had no herbicidal efficacy on rape except F 1 , suggesting that it be possible to find a kind of herbicides to inhibit dicotyledonous weeds in the field of dicotyledonous crops with the same genus as aforementioned weeds.

In the title mol­ecule, C19H15F3N2O, the benzene rings of the tolyl and trifluoro­methyl­phenyl groups form dihedral angles of 64.1 (2) and 38.5 (2)°, respectively, with the pyridazine ring. The CF3 group is disordered over two orientations, with site-occupancy factors of ca 0.56 and 0.44.