α-(Substituted-phenoxyacetoxy)-α-heterocyclylmethylphosphonates: Synthesis, Herbicidal Activity, Inhibition on Pyruvate Dehydrogenase Complex (PDHc), and Application as Postemergent Herbicide against Broadleaf Weeds

Pyruvate dehydrogenase complex (PDHc) is the site of action of a new class of herbicides. On the basis of the previous work for O,O'-dimethyl alpha-(substituted-phenoxyacetoxy)alkylphosphonates (I), further synthetic modifications were made by introducing a fural and a thienyl group to structure I. A series of alpha-(substituted-phenoxyacetoxy)-alpha-heterocyclylmethylphosphonate derivatives (II) were synthesized as potential inhibitors of PDHc. The postemergent activity of the title compounds II was evaluated in greenhouse experiments. The in vitro efficacy of II against PDHc was also examined. Compounds II with fural as R-3 and 2,4-dichloro as X and Y showed significant herbicidal activity and effective inhibition against PDHc from plants. O,O'-Dimethyl alpha-(2,4-dichlorophenoxyacetoxy)-alpha-(furan-2-yl)methylphosphonate II-17 had higher inhibitory potency against PDHc from Pisum sativum than against PDHc from Oryza sativa in vitro and was most effective against broadleaf weeds at 50 and 300 ai g/ha. II-17 was safe for maize and rice even at the dose of 900-1200 ai g/ha. Field trials at different regions in China showed that II-17 (HWS) could control a broad spectrum of broad-leaved and sedge weeds at the rate of 225-375 ai g/ha for postemergent applications in maize fields. II-17 (HWS) displayed potential utility as a selective herbicide.