Design, Efficient One-Step Synthesis of Bromo-p-hydroxybenzamides and Herbicidal Activity Evaluation

Discovering super-efficient herbicides with novel structures is one of the effective ways to solve the increasingly severe weed resistance problem and meet ecological requirements. In this work, a series of novel bromo-p-hydroxybenzamides were designed based on the molecular hybridization strategy, and rapidly synthesized by one-step amidation reaction, and then characterized by ¹H NMR, ¹³C NMR and HRMS. The herbicidal activity assay indicated that most of the target compounds exhibited good-to-excellent inhibition effects on seed germination of two model plants. At a concentration of 100 mg/L, the inhibition rate of 3,5-dibromo-N-(4-bromo-3-chlorophenyl)-p-hydroxybenzamide reached up to 98 and 96% on the roots and stalks of the monocotyledonous barnyard grass (E. crus-galli), respectively. 3,5-Dibromo-N-(2-bromophenyl)-p-hydroxybenzamide showed excellent inhibitory activity on the roots and stalks of dicotyledonous rape (B. napus) at 100 mg/L, with an inhibitory rate of more than 90%. Furthermore, the concentration was reduced to 1 mg/L, the inhibitory rate of 3,5-dibromo-N-(2-bromophenyl)-p-hydroxybenzamide on the roots of B. napus was still as high as 90%. This work provides a novel molecular scaffold for the development and research of new super-efficient herbicides.