Synthesis and herbicidal activity of novel 6-arylthio-3-methylthio-1<i>H</i>-pyrazolo[3,4-d]pyrimidin-4(5<i>H</i>)-ones

<p>A series of pyrazolo[3,4-d]pyrimidine-4-one derivatives was conveniently synthesized via tandem aza-Wittig and annulation reactions of the corresponding iminophosphoranes, arylisocyanate, and substituted thiophenols. The structures of the target compounds were confirmed by IR, ¹H NMR, ¹³C NMR, LC-MS, and elemental analysis. The preliminary bioassay demonstrated that some title compounds such as 6-(3-chlorophenylthio)-1-phenyl-3-methylthio-5-(4-chlorophenyl)-1<i>H</i>-pyrazolo[3,4-d]-pyrimidin-4(5<i>H</i>)-one and 6-(4-fluorophenylthio)-1-phenyl-3-methylthio-5-(3-chlorophenyl)-1<i>H</i>-pyrazolo[3,4-d]pyrimidin-4(5<i>H</i>)-one showed good inhibition activities against the root of <i>Brassica napus</i> (rape) and <i>Echinochloa crusgalli</i> (barnyard grass) at a dosage of 100 mg/L.