Phenylpyrazole herbicides

Phenylpyrazole herbicides, e.g., the selective post-emergence cereal-selective herbicide pyraflufen-ethyl (115 1999, Ecopart , Nihon Nohyaku) [201]. 

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... 

Also published in 2004 were the synthesis and stmcture-activity of several 2- luoro-4-chloro-5-substituted-phenyl pyrrole Protox herbicides, such as compound 84 [95]. This interesting pyrrole class of chemistry further extends the stmcture-activity of the 2-fluoro-4-chloro-5-substituted-phenylpyrazoles fluazolate (17) and pyraflufen-ethyl (18) discussed in Section 3.2.2 (Fig. 3.22). 

Fiprole insecticides belong to the chemical class of insecticidal phenylpyrazoles (arylpyrazoles) [1], discovered independently by Bayer AG [2] and by May Baker, a subsidiary of Rhone-Poulenc [3-5], while studying herbicidal phenylpyrazoles (PPO-herbicides, Nipyraclofen) [6, 7]. 

Pyraflufen-ethyl [15] is CHF20-containing phenylpyrazole (Fig. 10). This compound is a post-emergence contact herbicide for the control of broadleaf weeds, including cleavers (Galium aparine), in cereals and cotton, which also shows excellent crop selectivity for wheat and barley. It is rapidly absorbed by the foliage of broadleaf weeds, resulting in necrosis and desiccation. 

Figure 6. Relative Herbicidal Activity of Chiral Phenylpyrazoles...

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