Preemergent herbicidal activity

Amino-2-bromoimidazoles (77) have been prepared by the action of hydrogen bromide on a-cyanoalkylcyanamides (74) and were found to display preemergent herbicide activity (64JOC153). These 4-aminoimidazoles (77) are unstable in the presence of water and undergo rapid decomposition on treatment with base. 

This is a relatively new class of preemergent herbicides active against most grass at economical rates, with very little activity towards broadleaf... 

In summary, with the discovery in Dow that a-(2,2,2-trichloroethyl) styrene possessed unique preemergent herbicidal activity and the synthesis and evaluation of close to one thousand related materials, a new product, tridiphane, the active ingredient in TANDEM will enter the marketplace in 1986. Tridiphane will be the first postemergent grass herbicide for use in corn and will be used in combination with triazine herbicides such as atrazine and cyanazine. 

Table I. Preemergent Herbicidal Activity and Inhibition of Hill Reaction (plso)...

Sugar herbicide RE 39571, 5,6-dideoxy-l,2-0-(l-methylethylidene)-3-0-(2-methylphenylmethyl)-a-D-xylo-hexofuranose (Figure 1), a representative of a novel series of chiral grass herbicides, has been demonstrated in our laboratories to possess a high level of preemergence herbicidal activity against grassy weeds with safety on soybeans, cotton, peanuts, and several other broadleaf crops. This herbicide has also been demonstrated to possess some broadleaf weed activity. 

Metazachlor is a selective preemergence herbicide active on a wide range of both broad-leaved and grass weeds. It can be used selectively in Brassica spp. crops including winter oilseed rape at a rate of 1-1.8 kg active ingredient/ha. 

As a methodology to search for a new lead, we focused on the chemical approach using A,S-heterocycles. This approach led to the evolution of 5-methylene-thiazolidines as the lead to bleaching herbicides. Further structural modifications based on the parent compound resulted in the creation of a new family of bleaching herbicides, 2-(W-difluoroacelylimino)-S-methyl-3-(3-trifiuoromethylphenyl)-l,3-thiazoline, (S-3085) widi potent preemergence herbicidal activity and selectivity on cotton crops. On die basis of biochemical studies, 3-phenylthiazolines have been characterized as a new inhibitor of phytoene desaturase. Facile syndieses of 1,3-thiazolines and the manufacturing process toward S-3085 will be reported in future publications. 

The results showed that pyridyl group as R was beneficial to the pre-emergence herbicidal activity when 4-F as Y . Among the U, U-5 exhibited the best preemergence herbicidal activity at 900 g ai/ha. 

As shown in Tables 2.48 and 2.49, IG-21 exhibited notable post-emergence herbicidal activity comparable to IC-22. Its herbicidal activity seems better than that of IH-13 and U-13. Both IC-22 and IG-21 would be promising for finther development as post-emergence herbicides, and IG-21 also displayed modest preemergence herbicidal activity against dicotyledons. 

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