Synthesis and Herbicidal Activity of 3-Aryl-5-(haloalkyl)-4-isoxazolecarboxamides and Their Derivatives

Abstract

A series of unique 3-aryl-5-(haloalkyl)-4-isoxazolecarboxamides have been prepared which exhibit, in both greenhouse and field studies, significant preemergent and postemergent herbicidal activity in the grams per hectare range against broadleaf and narrowleaf weeds. The key step in the formation of the fully substituted isoxazole ring 2 is 1,3-dipolar cycloaddition of a haloalkylsubstituted acetylenic ester and a nitile oxide intermediate. The 3-aryl-5-(haloalkyl)-4-isoxazole-carboxylate esters 2 are converted to isoxazole-4-carboxamide herbicides 5 and 6, secondary amides 7, and amino acid derivatives 8. Greatest activity was observed with compounds having a combination of three substituents: a substituted phenyl ring in the 3-position, a primary or secondary carboxamide in the 4-position, and a difluorochloromethyl group in the 5-position of the isoxazole ring