A number of 2-(substituted phenoxymethyl)phenyl-2-methoxy iminoacetamides were synthesized and their fungicidal activities were examined. The strength of activities and fungicidal spectra varied markedly depending upon the substituents on the benzene ring of the 2-phenoxymethyl group of phenylacetamide moiety. Incorporation of either one or two substituent(s) at 2-, 3-, 4-and/or 5-positions on the benzene ring resulted in an increase of fungicidal activity compared to the unsubstituted compound. However, introduction of a bulky substituent at the 2-position or simultaneous substitution at 2-and 6-positions resulted in decrease of activity. When 2-and 4-, or 2-and 5-positions of the benzene ring were substituted with chlorine and/or methyl groups, in addition to the 2, 5-difluoro derivative (30), the activities were excellent against wheat powdery mildew, cucumber powdery mildew, cucumber gray mold and cucumber downy mildew. Between the two geometrical isomers, the E-form was much stronger than the Z-form.
A number of a-alkoxyphenylacetic acid derivatives were synthesized and their fungicidal activities were examined. Studies of structure-activity relationships revealed strong fungicidal activity when the substituent at the a-position was a methoxy group and a substituted phenoxymethyl group was introduced to the 2-position of the benzene ring of the phenylacetic acid moiety. When a substituted phenoxy group was introduced to this position, the fungicidal activity was very weak. It was also shown that N-methylphenylacetamide derivatives had stronger activities than phenylacetic acid methyl ester derivatives. Among the compounds synthesized in this study, 2-[2-(2, 5-dimethylphenoxymethyl)phenyl] -2-methyl-Nmethylacetamide (35) showed the most potent fungicidal activity against a wide range of crop diseases.
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