Mild Nitration of Pyrazolin‐5‐ones by a Combination of Fe(NO3)3 and NaNO2: Discovery of a New Readily Available Class of Fungicides, 4‐Nitropyrazolin‐5‐ones

4‐Nitropyrazolin‐5‐ones have been synthesized by the nitration of pyrazolin‐5‐ones at room temperature by employing the Fe(NO3)3/NaNO2 system. The method demonstrated selectivity towards the 4‐position of pyrazolin‐5‐ones even in the presence of NPh and allyl substituents, which are sensitive to nit...

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Bibliographic Details
Published in:Chemistry : a European journal 2019-04, Vol.25 (23), p.5922-5933
Main Authors: Krylov, Igor B., Budnikov, Alexander S., Lopat'eva, Elena R., Nikishin, Gennady I., Terent'ev, Alexander O.
Format: Article
Language:English
Subjects:
Chemistry
Clotrimazole
crop protection agents
Fluconazole
Free radicals
fungicidal agents
Fungicides
Iron
Nitration
Nitrites
Nitrogen dioxide
nitrogen oxides
Pesticides
Phytopathogenic fungi
Plant protection
Reagents
Selectivity
Sodium nitrite
Synthesis
synthetic methods
Triadimefon
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Summary:4‐Nitropyrazolin‐5‐ones have been synthesized by the nitration of pyrazolin‐5‐ones at room temperature by employing the Fe(NO3)3/NaNO2 system. The method demonstrated selectivity towards the 4‐position of pyrazolin‐5‐ones even in the presence of NPh and allyl substituents, which are sensitive to nitration. It was shown that other systems containing FeIII and nitrites, namely Fe(NO3)3/tBuONO, Fe(ClO4)3/NaNO2, and Fe(ClO4)3/tBuONO, were also effective. Presumably, FeIII oxidizes the nitrite (NaNO2 or tBuONO) to form the NO2 free radical, which serves as the nitrating agent for pyrazolin‐5‐ones. The synthesized 4‐nitropyrazolin‐5‐ones were discovered to be a new class of fungicides. Their in vitro activities against phytopathogenic fungi were found comparable or even superior to those of commercial fungicides (fluconazole, clotrimazole, triadimefon, and kresoxim‐methyl). These results represent a promising starting point for the development of a new type of plant protection agents that can be easily synthesized from widely available reagents. Seek and destroy: A new class of potent and structurally simple fungicides has been discovered along with an original method for their preparation (see figure). The in vitro activities of the synthesized 4‐nitropyrazolin‐5‐ones against phytopathogenic fungi were found comparable or superior to those of commercial fungicides (fluconazole, clotrimazole, triadimefon, and kresoxim‐methyl).
ISSN:0947-6539
1521-3765
DOI:10.1002/chem.201806172