Herbicidal activity against broadleaf

The 0,0-dimethyl heterocyclylmethylphosphonates IG-IJ with fur-2-yl or thien-2-yl group as and 2,4-Cl2 as Y as well as that with pyrid-2-yl group as and 2-F or 4-F as Y were most beneficial to herbicidal activity. 0,0-Dimethyl 1-(2,4-dichlorophenoxyacetoxy)-l-(fur-2-yl)methylphosphonate IG-21 was found to be the most effective compound with excellent herbicidal activity against broadleaf weeds at 37.5 g ai/ha. IG-21 showed a good selectivity and safe for monocotyle-donous crops, such as maize and rice even at 0.9-1.2 kg ai/ha. IG-21 is promising for development as a selective post-emergence herbicide. 

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

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. 

Sulfonylureas in which a methylene linkage separates the orr/K>-carboxylate from the phenyl ring, such as phenylacetic ester 1, have also proven to be highly active herbicides, especially against broadleaf weeds in postemergence applications Q). 

G-32911, simetryn Simetryn was one of the first methylthiotriazine candidates tested, but was developed slowly until it was confirmed that rice had a higher crop tolerance to simetryn than to prometryn. It found its commercial place in the transplanted rice of Japan and in other countries in the subtropical rice belt. Simetryn is used to control broadleaf weeds in mixtures with other herbicides that are active against grasses. 

SAR analyses indicated that herbicidal activity could be increased greatly by optimizing r R, R, R" and Yn in phosphonate lo. 0,C>-dimethyl l-(2,4-dichlorophenoxyacetoxy)ethylphosphonate IC-22 (HW02, clacyfos) was found to be the most effective compound among lA—IF series against broadleaf in postemergence application at the rate of 18.75—450 g ai/ha (see Chap. 2). IC-22 also showed much higher and practical herbicidal activity than that of acylphosphinates or acylphosphonates 1. 

As shown in Scheme 2.2, the introduction of heterocyclic groups in R of IC-IF led to the phosphonates IG (R =fur-2-yl), IH (R =pyrid-2-yl) and IJ (R =thien-2-yl), respectively. The replacement of the substituted phenoxy moiety by the triazole ring in IB gave l-(l-phenyl-l,2,4-triazol-3-yloxyacetoxy) alkylphosphonates IK. Several compounds in IC and IG series were found to be herbicidally active compounds against broadleaf weeds by systematic study of alkylphosphonates lA-IK. 

IC-22 showed much higher herbicidal activity than that of those repoted plant PDHc inhibitors, acylphosphinates and acylphosphonates[l, 27]. Those compounds exhibited 80-100 % inhibition against weeds at 2.8 kg/ha but at this rate they had shown unacceptable phytotoxicity to the crops. Compared with acylphosphinates and acylphosphonates, IC-22 exhibited promising herbicidal activity and selectivity for development as a selective post-emergence herbicide which may be used for broadleaf weed control in monocot crop fields. 

In this section we describe the synthesis, herbicidal activity, and SAR analyses of heterocyclylmethylphosphonates IG-IJ. It has been found that IG-21 and some of its analogs have shown potential utility as an herbicide against broadleaf weeds. 

A detailed study of acylphosphinates and acylphosphonates showed that they were mechanism-based inhibitors of pyruvate dehydrogenase complex (PDHc) as analogues of pyruvate. However, these phosphinates and phosphonates were not active enough to be considered as herbicides [1-3]. As stated in Chap. 2, some 1-substituted alkylphosphonates IC and IG showed notable herbicidal activity. Furthermore, the substitution of R R, R, R" and Y in phosphonate lo could be directly relevant to their herbicidal activity. Among the 1-substituted alkylphosphonates lA-IC, IC-22 (clacyfos) was found to be most eflFective against broadleaf weeds as a competitive inhibitor of PDHc (Scheme 3.1) [4]. This result prompted us to study continually on the design of novel PDHc inhibitors as potential herbicides. 

Y =2,4-Cl2), nj-11 (R =Me, Y =2-Me,4-Cl), and IIJ-13 (RWPt, Y =2-Me,4-Cl) exhibited 80-100 % control against broadleaf weeds in post-emergence. Apparently, the di-substitution of 2- and 4-position on the phenoxy-benzene ring with 2,4-Cl2 or 2-Me,4-Cl as Y was beneficial to the herbicidal activity. Aminium salt UJ-ll and m-24 were found to show 60 % control against barnyard grass at 150 g ai/ha. 

He HW, Peng H, Wang T et al (2013) a-(Substituted-phenoxyacetoxy)-a-heterocyclylmethyl-phosphonates synthesis, herbicidal activity, inhibition on pyruvate dehydrogenase complex (PDHc), and application as postemergent herbicide against broadleaf weeds. J Agric Food Chem 61 2479-2488... 

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