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A computer-assisted retention prediction system (RPS) of fifteen O-ethyl O-aryl N-isopropyl phosphoramidothioates (1) in reversed-phase HPLC was investigated. The system is based on the use of four physicochemical parameters (hydrophobicity II, electric effect σ, field effect F and steric effect Es) which is closely related to the retention mechanism in reversed-phase HPLC. The system was evaluated by comparing the measured retention data with the predicted ones. The predicted values were consistent with the measured values within a relative error of 11.5%.

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.

4-(3-Trifluoromethylphenyl)pyridazine is a new series of compounds with bleaching and herbicidal activities. Starting from ethyl 2-(3-trifluoromethylphenyl)acetate, an important intermediate 7 was synthesized in five steps with a moderate total yield of 51.5% in a safe and practical way. Twenty-six novel 3-N-substituted amino-6-methyl-4-(3-trifluoromethylphenyl)pyridazine derivatives were synthesized and evaluated through a Spirodela polyrrhiza test and greenhouse test. Some compounds can completely inhibit Chl at 1 microg/mL and exhibit equal or higher herbicidal activities with the commercial bleaching herbicide diflufenican against dicotyledonous plants at a rate of 75 g/ha.

A series of 2-cyano-3-methylthio-3-substituted methylaminoacrylates were synthesized as herbicidal inhibitors of photosystem II (PSII) electron transport, in order to estimate the effect of fluorine atom, pyridyl group, chirality and ester chain on activity. The important intermediate 2-fluoro-5-aminomethylpyridine was synthesized with high yield. The bioassay results showed that most of title compounds had high herbicidal activity in postemergence treatment. The introduction of an α-methyl into the 3-substituted methylamino could improve the activity notably. The replacement of hydrogen by chlorine or fluorine group and phenyl by pyridyl group showed different effects, and at the same time, the ester chain affected the activity too.

A novel coupling reaction of 4-amino-5-mercapto-3-substituted-1,2,4-triazoles to generate symmetrically substituted hydrazines, N,N′-bis(5-mercapto-3-substituted-1,2,4-triazol-4-yl)hydrazines was unexpectedly observed. Five examples are presented to demonstrate this reaction. All isolated products were unambiguously characterized.

Two series, totaling twelve, of new compounds, ethyl 1-aroyl/(aroylmethyl)-5-methyl-3-methylthiopyrazole-4-carboxylates (5/6), have been synthesized via highly regioselectively acylation and alkylation reactions of ethyl 3-methyl-5-methylthio-1 H-pyrazole-4-carboxylate (2a) with aroyl chloride (3) and eco-friendly reagents alpha-tosyloxysubstituted acetophenones (4), respectively, and a green protocol has been developed. The acylation reactions were carried out under ultrasound irradiation, and the alkylation reactions were under microwave irradiation and ultrasound irradiation, respectively. Conventional reaction conditions, as well as the use of alpha-bromosubstituted acetophenone (4′) have also been applied in the synthesis of some randomly selected compounds in both series and have generated identical compounds correspondingly. Unexpected structures of compounds were unambiguously determined by X-ray crystallographic analysis.

The title compound, C16H23N5O3S, ethyl 5-amino-l-(5′-methyl-l'-t-butyl-4′-pyrazolyl)carbonyl-3-methylthio 1H-pyrazole-4-carboxylate (5) has been synthesized by the treatment of ethyl 2-cyano-3,3-dimethylthioacrylate with 1 -t-butyl-5-methyl-4-hydrazinocarbonylpyrazole (4) in refluxed ethanol. The possible mechanism of the above reaction was also discussed. The results of biological test show that the title compound has fungicidal and plant growth regulation activities.

The crystal structure of the title compound, C18H20N6O3, is stabilized by N—H...O and N—H...N hydrogen bonds.

The title molecule, C17H25N5O3S2, belongs to the family of bis-heterocycles. In the crystal structure, there are one intra- and two intermolecular hydrogen bonds. One of the two pyrazole rings and the six-membered ring formed by the intramolecular hydrogen bond are approximately coplanar.

In the crystal structure of the title compound, C20H20N2O4, the mol­ecules are linked by a weak inter­molecular C—H⋯N hydrogen bond. The molecule has crystallographic twofold rotation symmetry.

The title compound, C16H15F3N2O3, is composed of a 3-(tri­fluoro­methyl)­phenyl ring and a pyridazinone ring, which are approximately coplanar, and an ethyl acetate group on the pyridazinone ring. In the crystal structure, centrosymmetric­ally related mol­ecules form dimers through non-classical intermolecular C—H⋯O hydrogen bonds.

The tetra­hydro­pyrimidine ring of the title mol­ecule, C12H14N2OS, adopts a half-chair conformation. In the crystal structure, the mol­ecules are linked to form centrosymmetric­ally related hydrogen-bonded dimers.

The tetra­hydro­pyrimidine ring of the title mol­ecule, C11H11ClN2OS, adopts a half-chair conformation. In the crystal structure, the mol­ecules are linked to form centrosymmetric hydrogen-bonded dimers.

The title compound, C15H17NO4, is a potent new herbicide containing the pyrrolidine-2,4-dione ring system. In the crystalline state, the molecular skeleton contains one enol grouping, which is intramolecularly hydrogen bonded to a neighboring keto O atom.

The title compound, C18H15NO3, is a potent new herbicide containing the pyrrolidine-2,4-dione ring system. In the crystalline state, the molecular skeleton contains one enol hydrogen-bonded moiety, formed from benzoyl Czdbnd;O isomerization.

In the title compound, C(22)H(19)F(3)N(2)O(3), the benzene rings of the trifluoro-methyl-phenyl and benzoyl-phenyl groups form dihedral angles of 41.89 (10) and 67.44 (10)°, respectively, with the pyridazine ring. The methyl-propanoate group is nearly coplanar with the attached benzene ring [dihedral angle = 3.9 (2)°]. The trifluoro-methyl group is disordered over two positions; the site-occupancy factors are ca 0.64 and 0.36. In the crystal structure, inversion-related mol-ecules are linked through C-H⋯O hydrogen bonds and C-H⋯π inter-actions.

A series of pyrazolo[5,1-d][1,2,3,5]tetrazin-4(3H)one derivatives were designed, synthesized, and evaluated for their herbicidal activities where some of these compounds provided >80% control of Brassica campestris at 10 microg/mL. Quantitative structure-activity relationship studies were performed on these compounds using physicochemical parameters (electronic, Verloop, or hydrophobic) as independent parameters and herbicidal activity as a dependent parameter, where herbicidal activity correlated best (r > 0.8) with physicochemical parameters in this set of molecules. The herbicidal activity against B. campestris was mainly affected by the molar refractivity (MR) for R1, Taft (Eso) for R2 or R6, Verloop (Lm) for R3 or R5, and electronic parameters (Hammett's constants) for R4. The optimal MR for herbicidal activity is 0.95. The herbicidal activity against Echinochloa crus-galli was mainly related with the substituents' hydrophobic parameter. The optimal pi parameters for R1 and R4 for herbicidal activity are 0.72 and 0.68, respectively. In general, these compounds showed greater herbicidal activity toward B. campestris than E. crus-galli.

A series of pyrrolidine-2,4-dione and piperidine-2,4-dione derivatives were prepared and evaluated for their herbicidal activities where some of these compounds exhibited good bioactivity against Echinochloa crus-galli in comparison with sulcotrione. Quantitative structure-activity relationship studies were performed on these compounds using physicochemical parameters (hydrophobic, electronic, and Taft) as independent parameters and herbicidal activity as a dependent parameter, where herbicidal activity correlated best (r > 0.8) with hydrophobic (pi(o) + pi(p)), steric (Es), STERIMOL (B4), indicator (H(M)), van der Waals volume (V), and electronic parameter (sigma(m) + sigma(p)) in this set of molecules; the optimum van der Waals volume for R(2) is about 41.8 A3; when B4 is equal to 3, the target molecule possessed the lowest herbicidal activity.

A series of 3-[(α-hydroxy-substituted) benzylidene]pyrrolidine-2,4-dione derivatives were synthesized as candidate herbicides by reacting different aroyl acetates with N-substituted glycine esters. The new compounds were identified by 1H NMR spectroscopy and elemental analyses. Their herbicidal activities were evaluated. Some compounds exhibited excellent herbicidal activities at a dose of 187.5 g/ha. A suitable electron-donating substituent at the 2- and/or 4-position of the phenyl ring was essential for high herbicidal activity, a result that has not been reported before. It was also found that the title compound's structure−activity relationships were different from those of other similar kinds of earlier compounds, a result that may depend on the enol structure difference. Keywords: Herbicide; aroyl acetate; HPPD; electron-donating group; structure−activity relationship (SAR)

In the title compound, C13H17N5O2, the dihedral angle angle between the pyrazole and pyridazine rings is 14.44 (8)°. The mol­ecules are linked into a chain along the b axis by C—H⋯O hydrogen bonds.

In the title mol­ecule, C18H18ClN5O2, the central pyrazole ring is perpendicular to the benzene ring and approximately perpendicular to the pyridazine ring [dihedral angles 89.9 (2) and 82.8 (2)°, respectively].

In the title compound, C18H18ClN5O2, there are two independent mol­ecules in the asymmetric unit. In both mol­ecules, the pyrimidine ring is almost coplanar with the central pyrazole ring, while the benzene ring is almost perpendicular to it.

The title compound, C11H9ClN2O2, crystallizes with weak inter­molecular N—H⋯O hydrogen-bond inter­actions. The dihedral angle between the pyrimidine and benzene rings is 86.82 (7)°.

The pyrazolo[1,5-a]pyrimidine ring system of the title compound, C15H12N4S, is essentially planar and the dihedral angle between the plane of the pyrazolo[1,5-a]pyrimidine system and the plane of the phen­yl ring is 134.6 (7)°.

The title mol­ecule, C11H9FN2O, was synthesized from 3,6-difluoro­pyridazine, benz­yl alcohol and sodium hydro­xide in CH3CN under reflux. The asymmetric unit contains two independent mol­ecules with nearly identical geometry. In the crystal structure, the mol­ecules are linked by weak inter­molecular C—H⋯F hydrogen bonds and C—H⋯π inter­actions.

In the title compound, C14H15ClN2O, the benzene and pyrimidine rings are nearly perpendicular, the dihedral angle between them being 84.7 (2)°.

In the crystal structure of the title compound, C9H9ClN4, there are non-classical intramolecular C—H⋯N hydrogen bonds and intermolecular C—H⋯π interactions.

The tetra­hydro­pyrimidine ring of the title mol­ecule, C11H11FN2OS, adopts a half-chair conformation. In the crystal structure, the mol­ecules are linked to form centrosymmetric hydrogen-bonded dimers.

The title compound, C12H16N4O4S, is composed of two substituted pyrazole rings, which are connected through a sulfone group. The dihedral angle between the two pyrazole rings is 79.1 (1)°. The ethoxy­carbonyl substituent is planar and is slightly twisted away from the attached pyrazole ring.

The title compound, C15H13F3N2O, contains one benzene ring, one cyclohexane ring and a pyridazine ring. The dihedral angle formed by the pyridazine ring with the benzene ring is 61.5 (2)°. The crystal structure is stabilized by two intermolecular hydrogen bonds (N—H...O and C—H...F). The cyclohexane ring adopts a screw-boat conformation. The CF3 group is disordered over two positions; the site occupancy factors are ca 0.6 and 0.4.

The title compound, C24H27N3O4, also known as fenpyroximate, is a commercial acaricide. The benzene ring of the phenoxy group is approximately perpendicular to the pyrazole ring with a dihedral angle of 84.37 (11)°. The dihedral angle between the phenoxy and the benzoate benzene rings is 48.83 (8)°.