Application of Sustainable Natural Bioresources in Agriculture: Iodine-Mediated Oxidative Cyclization for Metal-Free One-Pot Synthesis of N-Phenylpyrazole Sarisan Analogues as Insecticidal Agents.

Abstract

In view of potential agricultural activity of sarisan (isolated from many plants or easily synthesized from sesamol, another biorenewable natural product) analogues, many research studies on the application of these biorenewable and abundant natural resources have been proceeded. A series of novel sarisan analogues containing N-phenylpyrazole were synthesized and evaluated for their insecticidal activity against a crop-threatening insect pest, Mythimna separata Walker. Meanwhile, an iodine-mediated oxidative intramolecular C–N bond formation methodology has been established for the one-pot synthesis of these N-phenylpyrazole-containing sarisan analogues. This practical one-pot methodology is metal-free and requires no separation of the less stable intermediate hydrazones. In addition, it was found that compounds 8l–r exhibited more promising insecticidal activity with the final mortality rates (FMRs) >62.1%, when compared with the positive control toosendanin. Especially, compound 8r with 2-fluoro-4-bromophenyl showed the most potent insecticidal activity, the FMR of which was 79.3%. On the basis of this, some interesting results of structure–activity relationships were also discussed.