One-Pot Regioselective Synthesis of Novel Oximino Ester-Containing 1-Aryl-4-chloro-3-oxypyrazoles as Potential Fungicides

A novel, functional‐group‐tolerant, and highly regioselective one‐pot synthesis of six 4‐chloro‐1‐aryl‐3‐oxypyrazoles, 8a–8f, containing an oximino ester moiety has been developed. Their structures were characterized by 1H‐ and 13C‐NMR, IR, MS, and elemental analyses. The regioselectivity of the reaction was also determined by single‐crystal X‐ray diffraction analysis of product 8d. The reaction pathway, proposed with the aid of DFT calculations, likely proceeds via a DMF‐catalyzed mechanism, which involves an electrophilic attack by SOCl2 and two nucleophilic substitutions by benzyl bromide (BnBr) and Cl−, respectively, as the key steps. A preliminary in vitro bioassay indicated that most compounds exhibited good fungicidal activities against Sclerotinia sclerotiorum and Gibberella zeae. Especially, 8d and 8e displayed higher or similar fungicidal activities compared with pyraclostrobin at the concentration of 10 μg/ml.