Synthesis and Herbicidal Activity of α‑(Substituted Phenoxybutyryloxy or Valeryloxy)alkylphosphonates and 2‑(Substituted Phenoxybutyryloxy)alkyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-one

On the basis of our work on the modification of alkylphosphonates 1, a series of α-(substituted phenoxybutyryloxy or valeryloxy)­alkylphosphonates (4–5) and 2-(substituted phenoxybutyryloxy)­alkyl-5,5-dimethyl-1,3,2-dioxaphosphinan-2-one (6) were designed and synthesized. The bioassay results indicated that 14 of title compounds 4 exhibited significant postemergence herbicidal activity against velvetleaf, common amaranth, and false daisy at 150 g ai/ha. Compounds 5 were inactive against all tested weeds. Compounds 6 exhibited moderate to good inhibitory effect against the tested dicotyledonous weeds. Structure–activity relationship (SAR) analyses showed that the length of the carbon chain as linking bridge had a great effect on the herbicidal activity. Broad-spectrum tests of compounds 4-1, 4-2, 4-9, 4-30, and 4-36 were carried out at 75 g ai/ha. Especially, 4-1 exhibited 100% inhibition activity against the tested dicotyledonous weeds, which was higher than that of glyphosate.