Synthesis and QSAR of herbicidal 3-pyrazolyl alpha,alpha,alpha-trifluorotolyl ethers

Pyrazole nitrophenyl ethers (PPEs) were recently identified as a novel class of chemistry exerting herbicidal effects by inhibition of protoporphyrinogen IX oxidase. This area of chemistry has been extended to include herbicidal pyrazolyl fluorotolyl ethers. In these compounds, a trifluoromethyl group substitutes for the 4'-nitro group found in the original herbicides and in ''classical'' nitrodiphenyl ether hebicides. Fluoroanisole pyrazole ethers, in which a trifluoromethoxy group replaces the nitro group of diphenyl ether herbicides, are also described. The shift from 4'-nitro to 4'-trifluoromethyl substitution, which is conservative in terms of electrostatics, produced a novel class of herbicide with substantial pre-emergent activity on narrowleaf weed species. Quantitative structure/activity relationships obtained with respect to substitution on the pyrazole ring and at the 3'-position of the fluorotolyl moiety can be summarized effectively by comparative molecular field analysis. In general, 5-methanesulfonyl fluorotoluidide ethers were found to be most active.