Chapter 8
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N-Azolyl Phenoxypyrimidine Herbicides: Novel Inhibitors of Carotenoid Biosynthesis Part I Thomas P. Selby, Joseph E. Drumm, Reed A. Coats, Frank T. Coppo, Stephen K. Gee, James V. Hay, Robert J. Pasteris, and Thomas M. Stevenson Stine-Haskell Research Center, DuPont Crop Protection, Newark, DE 19714
Substituted 2-azolyl-4-phenoxypyrimidines of formula 1 represent a new family of highly active herbicides that act by inhibiting carotenoid biosynthesis. Azole substituents on the pyrimidine are nitrogen-linked and include pyrazole, imidazole and triazole. These compounds are active preemergence and postemergence but tend to be more active preemergence. Selectivity was observed on wheat, corn, and soybeans. There was particular interest in these compounds as cereal herbicides for preemergent and early-postemergent weed control. High field efficacy was observed, particularly on broadleaf weeds. Pyrazolylpyrimidine 1a showed optimum activity in cereal field trials and gave excellent broadleaf weed control at rates as low as 5-10 g/ha, with good wheat safety. This paper will focus on chemistry, biology, structure-activity relationships, mode-of-action, and field activity for compounds of this herbicide class.
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© 2002 American Chemical Society In Synthesis and Chemistry of Agrochemicals VI; Baker, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2001.
Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: July 29, 2001 | doi: 10.1021/bk-2002-0800.ch008
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Previously, 2-aryl-4-phenoxypyrimidines such as 2 (7) were investigated as herbicides at American Cyanamid. More recently at DuPont, novel 2azolyl-4-phenoxy-pyrimidines of formula 1 were also found to be highly active herbicides (2). Azole substituents (where X and Y are Ν and/or CR) on the pyrimidine core of 1 are nitrogen-linked and include pyrazole, imidazole and triazole. These compounds were shown to act by blocking carotenoid biosynthesis and were of special interest as preemergent and early postemergent cereal herbicides for broad-spectrum weed control. Pyrazolylpyrimidine l a was found to provide optimum weed control at very low rates of application in field trials, with good wheat safety. In this paper, we focus on the chemistry, biology, structure-activity relationships, mode-ofaction, and field activity for novel compounds of formula 1.
Chemistry Our initial method for making 4-phenoxy-2-pyrazolylpyrimidines was non-regioselective and gave rise to isomeric products as summarized in Figure 1. Reaction o f 2,4-dichloropyrimidines o f formula 3 with commercially available 3-trifluoromethylpyrazole and potassium carbonate in N,Ndimethylformamide gave mixtures of 2-chloro-4-pyrazolylpyrimdines of formula 4 and 4-cMoro-2-pyrazolylpyrimidines of formula 5 in yields o f 5060% and
