Synthesis and Bioactivities of Novel Pyrazole Oxime Derivatives Containing a 5-Trifluoromethylpyridyl Moiety

Abstract

In this study, in order to find novel biologically active pyrazole oxime compounds, a series of pyrazole oxime derivatives containing a 5-trifluoromethylpyridyl moiety were synthesized. Preliminary bioassays indicated that most title compounds were found to display good to excellent acaricidal activity against Tetranychus cinnabarinus at a concentration of 200 μg/mL, and some designed compounds still showed excellent acaricidal activity against Tetranychus cinnabarinus at the concentration of 10 μg/mL, especially since the inhibition rates of compounds 8e, 8f, 8l, 8m, 8n, 8p, and 8q were all 100.00%. Interestingly, some target compounds exhibited moderate to good insecticidal activities against Plutella xylostella and Aphis craccivora at a concentration of 200 μg/mL; furthermore, compounds 8e and 8l possessed outstanding insecticidal activities against Plutella xylostella under the concentration of 50 μg/mL.

Keywords: 5-trifluoromethylpyridyl; bioactivity; pyrazole oxime; synthesis.

Figure 1

The design of the target molecules.

Scheme 1

Synthesis of the title compounds 8a–8w. Reagents and conditions: (a) 4-hydroxybenzaldehyde, Cs₂CO₃, N,N-dimethylformamide, 105 °C for 10 h, 75% for 2; (b) NaBH₄, ethanol, 0 °C for 3 h, 90% for 3; (c) thionyl chloride, N,N-dimethylformamide, dichloromethane, r.t. for 8 h, 82% for 4; (d) NaOR (R = Me, Et and t-Bu), ROH, 30 °C for 3 h, 45 °C for 2 h, 41%–49% for 6a–6c; NaOR (R = substituted phenyl), dimethylsulfoxide, 105 °C for 4–15 h, 60%–81% for 6d–6w; (e) hydroxylamine hydrochloride, potassium hydroxide, methanol or ethanol, reflux for 6–16 h, 65%–87% for 7a–7w; (f) compound 4, Cs₂CO₃, acetonitrile, reflux for 10–18 h, 44%–63% for 8a–8w.