Synthesis and herbicidal activity of novel 5-chloro-3-fluoro-2-phenoxypyridines with a 1,3,4-oxadiazole ring

Abstract

A series of novel 5-chloro-3-fluorophenoxypyridines with a 1,3,4-oxadiazole ring bearing a thioether moiety was synthesized and their herbicidal activity against some graminaceous plants and crop safety were examined. Target compounds were prepared through S-substitution reaction of 5-mercapto-1,3,4-oxadiazole analogs, which were synthesized by the reaction of 2-propynyl (R)-2-[4-(5-chloro-3-fluoro-pyridin-2-yloxy)-phenoxy]propionate with hydrazine hydrate and the subsequent reaction with carbon disulfide. The newer 3,5-dihalophenoxypyridines and the intermediate, 5-chloro-3-fluoro-2-{4-[(R)-1-(5-mercapto-1,3,4-oxadiazol-2-yl)ethoxy]phenoxy}pyridine, were characterized using 1H NMR, 13C NMR, IR spectroscopy and elemental analysis. Almost all 5-chloro-3-fluorophenoxypyridines showed a moderate to high level of activity against all weeds tested at 125 g/ha application. In particular, 5-chloro-3-fluoro-2-(4-{(R)-1-[5-(2-propynylthio)-1,3,4-oxadiazol-2-yl]ethoxy}phenoxy)pyridine exhibited potent activity without crop injury. © Pesticide Science Society of Japan.