Oxadiazole herbicides

Oxadiazole herbicides, e.g., the pre- and post-emergence rice herbicide oxadiargyl (120 1996, Raft , BayerCropScience)... 

Others have found little correlation between the herbicidal effects and the amount of PPIX accumulated by Protox-inhibiting herbicides (50, 64). In cucumber (Fig. 4), pigweed, and velvetleaf, we found a strong correlation between the amount of PPIX accumulated in response to acifluorfen and the amount of ensuing herbicidal damage (41). Also, there was an excellent correlation between the PPIX and the resulting herbicidal damage caused by a variety of diphenyl ether and oxadiazole herbicides (41). 

Oxadiazole, 2,5-diaryl-electrophilic substitution, 6, 438 as fluorescent whitener, 6, 446 herbicidal activity, 6, 445... 

The herbicide activity ascribed to the 1,2,4-oxadiazole derivative 67 (60) has prompted the search for other biologically active derivatives. This example was prepared from the corresponding 5-chloromethyl-1,2,4-oxadiazole 63 via conversion to the HHT 65 through the aminomethyl analog 64. Reaction of the HHT 65 with diethyl phosphite under neat conditions produced the desired diethyl ester intermediate 66, which was hydrolyzed to 67. 

The relationship between the herbicidal activity of 1,2,5-oxadiazole iV-oxides and some physicochemical properties potentially related to this bioactivity, such as polarity, molecular volume, proton acceptor ability, lipophilicity, and reduction potential, were studied. The semi-empirical MO method AMI was used to calculate theoretical descriptors such as dipolar moment, molecular volume, Mulliken s charge, and the octanol/water partition coefficients (log Po/w) <2005MOL1197>. 

The applications of 1,2,5-oxadiazole iV-oxide and benzo[c][l,2,5]oxadiazole iV-oxide derivatives as compounds which have herbicidal activity are known. For example, the most active compound, butylcarbamoylbenzoL] 1,2,5-oxadiazole iV-oxide, displayed herbicidal activity at concentrations as low as 24 gha-1 <2000JFA2995>. The preparation of 5,7-disubstituted 4,6-dinitrobenzofuroxane derivatives (2-chlorophenylamino, 2,5-dichlorophenyl-amino, 2-hydroxyphenylamino, or 4-bromophenylamino), which are useful as agricultural arachnicides and bactericides, was described <2005RUP2255935>. 

Examples of the many oxadiazolinones which show herbicidal activity (weed killers) are (118e), (118f), and oxadiazon (118g), which is the subject of many regular reports in the literature. Insecticidal activity is shown by oxadiazolinones (118h), (1181), (the latter is an aphicide), and oxadiazole (117h). 

Numerous other five-membered heterocycles have been found to produce herbicidal effects (74ZN(C)232), such as pyrazolones, thiadiazolones, polyhaloimidazoles and 1,3,4-oxadiazol-2-ones, an important example of which is oxadiazon (14) (68BRP1110500). This is synthesized by cyclization of the 2-(pivaloyl)phenylhydrazine (15) with carbonyl chloride (Scheme 5). 

A variety of 2,5-diaryl-, 2,5-dialkyl- and 2-alkyl-5-aryl-l,3,4-oxadiazoles show herbicidal activity, particularly against broad-leafed weeds and grasses in crops such as rice and corn (80JAP8027042, 76MIP42301). Several reports on a wide selection of herbicidal uses for oxadiazolinone (124) appear yearly in the recent literature. 

Trifluoroacetic acid or trifluoroacetic acid anhydride reacts with hydrox-amic acid amides, thiosemicarbazide, and 1,2-diaminopyridine to yield herbicidal active 1,2,4-oxadiazoles [78GEP(0)2801509], fungicidal-active 1,3,4-thiadiazoles (80USP4264616), and 2-trifluoromethyltriazolo[l,5-alpyridines [80JFC(15)179. 2-Trifluoromethyl-L-histidine was obtained from L-histidine on treatment with benzoyl chloride/sodium hydroxide and subsequent ring closure with trifluoroacetic anhydride (78JOC3403) (Scheme 41). 

Diary] and triaryl or naphthyl carbamates exhibit low herbicidal activity. The substitution of the aryl radical for a heterocyclic radical gives heterocyclic alkyl and dialkyl ureas, of which many examples have been prepared in recent years. The herbicidal activity of urea derivatives containing a heterocyclic radical, such as benzthiazole, thiazole, thiadiazole, oxadiazole and pyridine, is favourable if one or two methyl groups are substituted at the N -nitrogen. The carrier of total or selective action in these derivatives is presumably the heterocyclic part of the molecule. More recently several new groups of compounds have become known, mainly in the patent literature, for which the structure-activity on relationships are still to be elucidated. 

The compounds of the 3-alkylcarbamoyl-5-alkyl-l,3,4-oxadiazol-2-one group are insecticides, and the 3-phenylcarbamoyl-l,3,4-oxadiazol-2-one derivatives are fungicides, while the 5-r-butyl-3-phenyl-2-oxadiazolones are herbicides. 

BRN 0628305 3-(4-(5-t-Butyl-2,3-dihydro-2-oxo-1,3,4-oxadiazol-3-yl)-3-chlorophenyl)-1,1-dimethylurea 3-(4-(5-(tert-Butyl)-2-oxo-1,3,4-oxadiazol-3(2H)-yl)-3-chloro-phenyl)-1,1-dimethyiurea N -(3-Chloro-4-(5-(1,1-di-methylethyl)-2-oxo-1,3,4-oxadiazol-3(2H)-yl)phenyl)-N,N-dimethylurea Dimefuron Legurame TS Pradone kombi Pradone plus Pradone TS RP 23465 Urea, 3-(4-(2-t-butyl-5-oxo-A -1,3,4-oxadiazolin-4-yl)-3-chioro-phenyl)-1,1-dimethyl- Vt 2809, Herbicide. Crystals mp = 193" soluble in H2O (0.0016 g/100 ml), very soluble in CHCI3, soluble in Me2CO, CH3CN, acetophenone, EtOH, slightly soluble in CsHs, CzHs, xylene LDso (rat orl) > 2000 mg/kg, (mus orl) > 10000 mg/kg, (dog orl) > 2000 mg/kg, (rbt der) > 1000 mg/kg, (rat ip) n 4000 mg/kg LCso (rainbow trout, bluegill sunfish 96 hr.) > 1000 mg/l non-toxic to bees. Aventls Crop Science May Baker Ltd. Rhdne-Poulenc. 

Oxadiazoles, their A-oxides, as well as their benzo-hised systems, are biologically active compounds. Some of their derivatives are important because of their anthelmintic, fungicidal, bactericidal and herbicidal action. They have also been found to have antitumour activity. 

Several discoveries made in the 1960s had a significant impact on our understanding of the structure-activity of Protox herbicides. The first breakthrough was the discovery of the importance of the 2,4-dihalo-5-substituted-phenyl substitution pattern. Rhone-Poulenc first introduced 3-(2,4-dichlorophenyl)-l,3,4-oxadiazol-2(3H)-one (9) in 1965 [40]. Further structure-activity optimization at the phenyl ring soon led to the discovery in 1968 of the 2,4-dichloro-5-isopropoxyphenyl substitution pattern of the herbicide oxadiazon (2) [41, 42]. 

Phenyl tetrahydrophthalimides represent the third class of early Protox herbicides. They were introduced in the early 1970s, after the diphenyl ether and l,3,4-oxadiazol-2(3H)-one chemistries. Following the introduction by Mitsubishi of chlorophthalim (3) [27] in 1972, incorporation of the 2,4,5-trisubstituted-phenyl pattern in the 1980s resulted in the synthesis of highly active molecules such as S-23142 (12) [45], and S-23121 (20) [45, 56] (Fig. 3.8). 

Continuous study of oxyacetamide chemistry shifted research from the paddy herbicide to an upland herbicide with increasing water solubility that is suitable for such upland use. To this end, benzanellated analogues such as the benzothia-zole moiety of mefenacet were changed to simple five-membered heterocycles that contain at least one nitrogen atom to increase water solubility, and sulfur or oxygen atom to decrease lipophilicity, for instance thiazoles, thiadiazoles, oxazoles and oxadiazoles (Fig. 8.2). Consequently, many patent applications of the new class of heteroxyacetamide herbicides were disclosed [17, 18]. 

The class of PODA has been reviewed. Besides as polymers, 1,3,4-oxadiazole derivatives are used in medical and agricultural applications, e.g., in the field of chemotherapy or as herbicides and insecticides. ... 

Nitrophenyl)-1 3,4-oxadiazoles identified as herbicides through random screening, are described. 

During the course of synthesis on an in-house discovery program, 2-(2 -nitrophenyl)-1,3,4-oxadiazole, If synthetic intermediate, was found to be herbicidally active in our greenhouse screen. Because this compound afforded control of all of the weeds in our initial screen and exhibited selectivity towards corn and wheat it was selected for optimization (Table I). 

Among 1,2,5-oxadiazoles, their N-oxides as well as their benzo-fused systems are biologically active compounds which show anthelmintic, fungicidal, bactericidal, herbicidal, and antitumor properties. 

The application of fluorinated furazan is rather limited for synthesis and reactivity. Most studied derivative is 3-amino-4-trifluoromethyl-l,2,5-oxadiazole, which is commercially available. Nevertheless, in recent years, some perspective applications have been envisaged. In the agrochemical field a large library (more than 300 derivatives) of A-(4-triflnoromethyl-l,2,5-oxadiazol-3-yl)benzamides 257 has been prepared and considered for herbicidal activity [ 140], while l-(4-fluoro-1,2,5-oxadiazol-3-yl)pyrazole derivatives 258 were claimed as herbicides and plant growth regulators (Fig. 14) [141]. 

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