A novel series of substituted 2-acylimino-1,3-thiazolines was synthesized and their herbicidal activity against upland weeds and selectivity against crops was assessed. The structure-activity relationships were probed by substitution of the thiazoline nucleus and/or an imino group. Highest activity was seen with compounds which contain two substituents: a methyl group at the 5-position of the thiazoline nucleus and a trifluoroacetyl or a difluoroacetyl group on an imino moiety. Among the

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... ds examined, 2-(N-difluoroacetylimino)-5-methyl-3-(3trifluoromethylphenyl)-1,3-thiazoline applied at rates between 62.5 and 125 g a.i./ha, showed excellent broadspectrum pre-emergence herbicidal activity against grass and broadleaf weeds without injury to cotton.