Synthesis and fungicidal activity of fluorine-containing chlorothalonil derivatives

Fourteen new fluorine-containing chlorothalonil derivatives were synthesized by using intermediate derivatization method (IDM) in order to discover novel antifungal compounds for controlling corn rust. The structures of synthesized compounds were confirmed by 1H NMR, 13C NMR, 19F NMR, elemental analysis, HRMS and X-ray. The bioassay results indicated that compound 2,4,5-trichloro-6-(2,6-dichloro-4-[trifluoromethyl]phenylamino)isophthalonitrile (3j, Rn is 2,6-Cl2-4-CF3) had the optimal structure with best fungicidal activity against corn rust (98%, 70% controls) at 25 and 6.25 mg/L concentration, respectively, much better than chlorothalonil and fluazinam, highlighting the importance of trifluoromethyl group on 4-position of benzene ring. The structure–activity relationship of the synthesized compounds was discussed as well.