Synthesis and structure‐activity relationships of 1‐aryl‐4‐substituted‐1,4‐dihydro‐5H‐tetrazol‐5‐ones, a novel class of pre‐ and post‐emergence herbicides

L‐Aryl‐4‐substituted‐1,4‐dihydro‐5H‐tetrazol‐5‐ones (I) represent a new class of herbicides, which, when applied pre‐ or post‐emergence in the presence of light, control several agriculturally important weed species. Forty‐eight analogues have been synthesized and their herbicidal activities determined in order to study structure‐activity relationships. In general, these compounds demonstrated: (l) optimum herbicidal activity when the 4‐ substituent on the tetrazole ring was – CH2CH2CH2F, and the aryl group 2‐ fluoro‐4‐chloro‐5‐substituted phenyl; (2) optimum herbicidal activity over a broad spectrum of grass and broad leaf weeds, with marginal crop selectivity when the C5 substituent on the phenyl group was – OCH2CCH; and (3) a high degree of selectivity on several major crops and primarily broadleaf weed control when this substituent was – NHSO2CH2CH3.