One‐pot synthesis, structure and structure–activity relationship of novel bioactive diphenyl/diethyl (3‐bromo‐1‐(3‐chloropyridin‐2‐yl)‐1 H ‐pyrazol‐5‐yl)(arylamino)methylphosphonates

BACKGROUND N ‐Pyridylpyrazole derivatives have received continuous attention in agrochemical research during the last decade owing to their remarkable insecticidal or fungicidal potentials. To look for novel heterocyclic agrochemicals for increasing production of agriculture, a series of novel α ‐aminophosphonate derivatives containing N ‐pyridylpyrazole moiety were synthesized. RESULTS The structures of the title compounds were confirmed via melting point, IR, 1 H NMR, 13 C NMR, 31 P NMR, HRMS and elemental analysis. The single crystal structure of diethyl (3‐bromo‐1‐(3‐chloropyridin‐2‐yl)‐1 H ‐pyrazol‐5‐yl)(2,6‐dimethylphenylamino)methylphosphonate (compound 12b) was first reported. Moreover, the bioassays displayed that the title compounds exhibited modest or weak insecticidal activities against oriental armyworm at 200 μg mL −1 . The first investigation on the fungicidal potential of chlorantraniliprole showed no significant activities towards the six tested fungi found in this study, however, most of the title compounds displayed apparent in vitro fungicidal activity against some plant fungi, in particular excellent activities towards Physalospora piricola . Compounds 11a and 11b had EC 50 values of 18.8 and 17.4 μg mL −1 , respectively, which were comparable with that of fungicide control triadimefon (EC 50  = 24.7 μg mL −1 ) against Physalospora piricola . In addition, some compounds exhibited modest in vivo control efficacy at 0.5 mg mL −1 towards Sclerotinia sclerotiorum (11b: 30.1(±1.8)%), Rhizoctonia cerealis (11a: 20.4(±2.1)%; 11b: 30.2(±2.2)%), and Erysiphe graminis (11a: 30.3(±1.8)%; 12d: 40.2(±0.9)%). CONCLUSION Compounds 11a, 11b and 12d could be promising new lead structures for the development and discovery of novel fungicides towards Physalospora piricola and Erysiphe graminis . The structure‐activity relationship (SAR) analysis provided useful guidance and new understanding for the design of novel pyridylpyrazole‐containing agrochemicals. © 2019 Society of Chemical Industry