Pyrazole herbicides

There are a number of other herbicides that affect photosynthesis indirectly. Pyrazole herbicides such as benzofenap, pyrazolynate and pyrazoxyfen interfere with chlorophyll biosynthesis and have found commercial application for the control of annual and perennial weeds in paddy rice and maize (Figure 2.4). 

Mode of Action of Pyrazole Herbicides Pyrazolate and Pyrazoxyfen HPPD Inhibition by the Common... 

Fig. 5. Concentration of metabolite in pyrazole herbicides solution used in HPPD assay. Error bars are SE of the means.

Synthesis and Herbicidal Activity of Enantiomeric Lactate Derivatives of Aryl-Pyrazole Herbicides... 

Extensive reviews have been pubUshed, covering the Hterature to about 1967 (1 3). Pyrazoles and the benzopyrazoles have been well reviewed in References 4 and 5. More up-to-date reviews, though much narrower in scope, have been pubUshed on pyrazole oxides (6), dihydropyrazoles as insecticides (7), the anticancer dmgs anthrapyrazoles (8,9), and pyrazole sulfonylureas as herbicides (10). 

The Knorr pyrazole synthesis has been extensively utilized in the preparation of a number of pyrazoles as metal chelators, photographic dyes, herbicides, and biologically active... 

N-Phenylpyrazolone 194a adds to indolones 213 to form spiro pyrano-pyrazoles 226, which possess herbicidal activity (88JIC277) (Scheme 86). 

A recent patent has reported the preparation of several l-(3-nitrophenyl) pyrazoles, as intermediates leading to potential herbicides, by nitration of some 1-arylpyrazoles of the type (29). This indicates meta nitration of a 1-arylpyrazole in yields of 88% (87JAP62/I23173). 

The 1-phenylpyrazole core has been shown to bestow pharmacological activity in a number of areas in the pharmaceutical and agrochemical industries. In the latter field, select examples of biological activities include insecticidal, miticidal, and herbicidal. More specifically, 1-phenylpyrazoles with alkyl, acyl, thioalkyl, or cyano substituents at the 4-position exhibit potent insecticidal activity. In particular, 5-amino-I-(2,6-dichloro-4-trifluoro-methylphenyl)-4-trifluoromethanesulfinyl-l//-pyrazole-3-carbonitrile (Fipronil ) is one of the most commercially successful insecticides. In fleas, ticks, and other arthropods, it acts as a gamma-aminobutyric acid (GABA)-gated... 

Phosphorus-containing Ring Systems. - A range of new chiral oxazaphospholidine oxides 266 and 267 have been synthesised and used as catalysts in asymmetric reductions of ketones with diborane. Mannich-type cyclisation reactions of 5-amino-3-benzylthio-4-cyano(ethoxycarbonyl)pyrazoles with dichlorophenylphosphine and aromatic aldehydes in the presence of cation exchange resin have been used to prepare a number of 6-oxo-6-phospha-4,5,6-trihydroimidazolo[l,2-b]pyrazoles, e.g. 268. Some of these compounds have herbicidal activity and this report is typical of a number of similar ones in the Chinese literature. A number of metallocycles, e.g. 269, have been reported as products from reactions of transient zirconocene-benzyne intermediates with phosphaimines followed by sulfuration or selenation. ... 

The Heck reaction makes a C-C bond and adds a highly functionalised fragment that can be elaborated into many other functional groups. The same is true of the Friedel-Crafts reaction that generally works well with azoles or other heterocycles able to do electrophilic substitution. As usual, it is best to have only one free position so that no regioselectivity problems arise. In the Heck reaction, the site of attack is marked by the iodine atom, but the Friedel-Crafts can occur at any free position. Our example is a pyrazole that acylates cleanly with Lewis acid catalysts to give eventually the herbicide pyrazolate 196. 

Pyrazol-3-ones have been tested and found useful as fungicides (99MI1), herbicides (96JAP(K)217777) and insecticides (99MI2). 

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