One‐pot Synthesis of 3‐phenyl‐4‐pyrazolylmethylene‐isoxazol‐(5H)‐ones Catalyzed by Sodium Benzoate in Aqueous Media under the Influence of Ultrasound Waves: A Green Chemistry Approach

Abstract

A series of 4-pyrazolylmethylene-3-phenylisoxazol-5(4H)-ones have been prepared from Knoevenagel condensation of pyrazole-4-carbaxaldehyde with isoxazolone precursors or via one-pot three-component cyclocondensation of pyrazole-4-carbaxaldehyde with β-ketoesters and hydroxylamine hydrochloride in the presence of sodium benzoate in water under the influence of ultrasonic waves. The merits of this method are efficient, clean, green, easy work-up, high yields, and shorter reaction time, and the catalyst could be recycled easily without affecting the catalytic activity.

Synthesis and characterization of novel biheterocyclic compounds from 3‐alkoxy‐1H‐pyrazole‐4‐carbaldehydes via multicomponent reactions

“…This result was supported by the 1 H-15 N HMBC spectrum, in which the protons from the 2,6-dimethyl moiety had a three-bond The synthesis of 4-[(pyrazol-4-yl)methylene]isoxazol-5(4H)-ones was carried out using a one-pot MCR of the pyrazole-4-carbaldehyde 3a, appropriate β-ketoester 6ae, and hydroxylamine hydrochloride (24) (Scheme 5). Several catalysts, such as piperidine, TEA, and sodium acetate [66], were tested, among which the latter was found to be the most effective. The MCR mixture was stirred in an ultrasonic bath at room temperature for 3 hours, and the 4-[(pyrazol-4-yl)methylene]isoxazol-5 (4H)-ones 25-29 were obtained in fair to good yields of 45-83%.…”

Catalytic Approaches to Multicomponent Reactions: A Critical Review and Perspectives on the Roles of Catalysis

“…This example of multicomponent synthesis showed the importance of studies on solvent effects and how these effects are associated with the catalytic action in the MCR. Although there are three possible mechanisms debated for ISX formation [ 169 , 170 , 171 , 172 , 173 , 174 , 175 ], the synthetic enzyme efficiently selected only one of them, as shown in Scheme 11 . Water proved to be the best solvent, likely due to its hydrogen bond acidity (α) ability.…”