Novel 2H-[1,2,4]thiadiazolo[2,3-a]pyrimidine derivatives bearing chiral S(−)-2-(4-chlorophenyl)-3-methylbutyric acid moiety: Design, synthesis and herbicidal activity

A series of S(−)-2-(4-chlorophenyl)-N-(5,7-disubstituted-2H-[1,2,4]-thiadiazolo[2,3-a]pyrimidin-2-ylidene)-3-methylbutanamide derivatives were designed and synthesized. The structures of all the newly synthesized compounds had been identified by elemental analysis, 1H NMR, MS and optical rotation. Their herbicidal activities were evaluated against a variety of weeds. The preliminary results showed that most of the target compounds had moderate inhibitory activities and selectivities against root and stalk of monocotyledon and dicotyledon plants. More importantly, the chiral target compounds showed improved herbicidal activities to some extent over their racemic counterparts against a variety of tested weeds, which might be contributed by the introduction of chiral active unit. The present work provided a novel class of chirality-based thiadiazolopyrimidine derivatives with potent herbicidal activities for further optimization.