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 1 H NMR, 13 C 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. Fig. 1. Synthetic Route of 5-chloro-3-fluoro-2-(4-[(R)-1-{5-(2-substituted thio)-1,3,4-oxadiazol-2-yl}ethoxy]phenoxy)pyridine.

Synthesis, Characterization, and Herbicidal Activities of New 1,3,4‐Oxadiazoles, 1,3,4‐Thiadiazoles, and 1,2,4‐Triazoles Derivatives Bearing (R)‐5‐Chloro‐3‐fluoro‐2‐phenoxypyridine

“…The purity of all compounds was confirmed on silica gel coated aluminum plates (Merck). The ester 1 was synthesized as previously reported method [21, 23].…”

“…As part of ongoing studies on the synthesis and biological consideration of heterocycles [19–22], we wish to report the synthesis of new series of 5‐membered heterocyclic titled compounds, bearing the ( R )‐5‐(1‐(4‐(5‐chloro‐3‐fluoropyridin‐2‐yloxy)phenoxy)ethyl) and their herbicidal activities.…”

Novel bisthioether derivatives containing a 1,3,4‐oxadiazole moiety: design, synthesis, antibacterial and nematocidal activities

“…It has recently been shown that the 1,3,4-oxadiazole ring, one of the most important and well-known heterocyclic nuclei, exhibits a wide variety of pesticidal biological activities, including antibacterial, [7][8][9][10][11][12][13] antifungal, [14][15][16][17][18][19][20][21] antiviral, [21][22][23] insecticidal, [24][25][26][27] and herbicidal. 28,29 In addition, in 2005, Guimarães et al demonstrated that introduction of a 1,3,4-oxadiazole ring into target compounds could change their polarity, flexibility and metabolic stability, effectively enhancing their bioactivity. 30 Meanwhile, we have previously described the synthesis and pesticidal biological properties of a series of 1,3,4-oxadiazole derivatives (Fig.…”

Design and Synthesis of 2,5‐Disubstituted‐1,3,4‐Oxadiazole Hybrids Bearing Pyridine and 1,2,3‐Triazole Pharmacophores

“…1,3,4‐Oxadiazoles, on the other hand, are well known in literature for their versatile biological activities such as anti‐inflammatory , vasodialatory , antibacterial , antifungal , antitumor , anticonvulsant , insecticidal and herbicidal . 1,3,4‐Oxadiazoles are also known as surrogates for carboxamides, esters and carboxylic acids to improve the biological activities of consequent molecules .…”