Synthesis and Herbicidal Activity of 2-(Substituted phenoxyacetoxy)alkyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-one

A series of 2-(substituted phenoxyacetoxy)alkyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-ones IIa-s were designed and synthesized on the basis of the previous work for the modification of alkylphosphonates I, and their structures were confirmed by H-1 NMR, P-31 NMR, C-13 NMR, IR, MS, and elemental analysis. Their herbicidal activities against seven species of weeds were evaluated in a greenhouse. A part of the title compounds such as IIa-g, Ilk, Ho, and Hr exhibited significant postemergence herbicidal activity against Abutilon theophrasti, Brassica juncea, Amaranthus retroflexus, and Eclipta prostrate at a dosage of 150 g ai/ha. Structure activity relationship analyses indicated that the introduction of a phosphorus-containing heterocyclic ring had a favorable effect on herbicidal activity, and their herbicidal activity could be further increased by a reasonable combination of X, Y, and R in parent structure II. It could be found that the title compounds Ha 2-[(2,4-dichlorophenoxy)acetoxy](methyl)methyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-one and Hr 2-[(4-chloro-2-methyl-phenoxy)acetoxy](methyl)methyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-one possess high activity and a broad spectrum against all of the test broadleaf weeds with 70-100% inhibition effect at a dosage of 75 g ai/ha, and the title compounds Ha and Hr are safe for corn and wheat at a dosage of 150 g ai/ha. Furthermore, the title compound Ha possesses low rat toxicity. These results suggest that the title compounds Ha and Hr could be potential and selective postemergence herbicides for further development.