A B S T R A C T l-Aryl-4-substituted-1,4-dihydro-5H-tetrazol-5-ones ( I ) represent a newclass of herbicides, which, when appEied pre-or post-emergence in the presence of light, control several agriculturally important weed species. Forty-eight analogues have been synthesized and their herbicidal activities determined in order to study structure-activity relationships. I n general, these compounds demonstrated: (1) optimum herbicidal activity when the 4substituent on the tetrazole ring was -CH,CH,CH,F, and the aryl group 2-~uoro-4-chloro-5-substituted phenyl; (2) optimum herbicidal activity over a broad spectrum of grass and broad leaf weeds, with marginal crop selectivity when the C5 substituent on the phenyl group was -OCH,C-CH;and (3) a high degree of selectivity on several major crops and primarily broadleaf weed control when this substituent was -NHSO,CH,CH,.
INTRODUCTIONA large number of herbicides are available to assist in controlling weeds in a variety of circumstances. These herbicides can be classified into families based on their chemical structure and mode of action.' Usually, each family of herbicides has associated with it a weed spectrum and crop selectivity that do not fluctuate greatly with structural changes of the molecule. This paper reports a new class of highly active herbicides of structure I (Fig. 1) whose weed spectrum and crop selectivity can be dramatically modified through manipulation of the substituent groups. The herbicidal activity of these compounds was optimized by varying the groups R,, R,, R, and R,. The nature of R, 259 Pestic. Sci. 0031-613X/90/$03.60 0 1990 SCI. Printed in Great Britain Procedure A: formation of methyl 2,4-disuhstituted benzoates. Methyl chloroformate (0.75 mol) was added dropwise to a mixture of 2,4disubstituted phenol (075 mol) and sodium hydroxide (0.75 mol) in water (150ml), while the temperature was kept below 10°C. The crystals that formed were collected and dried to give almost quantitative yields of the benzoate. With the exception of 4-chloro-2fluorophenol, which was synthesized according to a previously described method," all 2,4disubstituted phenols used in this procedure were commercially available.