Urea-catalyzed multicomponent synthesis of 4-arylideneisoxazol-5(4H)-one derivatives under green conditions

A simple and green one-pot, three-component procedure was used for the efficient synthesis of different isoxazol-5(4H)-ones from aryl/heteroaryl aldehydes, hydroxylamine hydrochloride, and beta-keto esters in environment-friendly water solvent containing a catalytic amount of urea. Employing urea as the commercially available and cost-efficient natural organo-catalyst provides an easy access to a large number of 3, 4-disubstituted isoxazol-5(4H)-one derivatives. The reaction proceeds well when electron-donating groups are present on the phenyl ring of substituted benzaldehydes, while only small amounts of heterocyclic products are obtained in the presence of electron-accepting groups on the benzene ring. In addition, the reaction occurs in water as an effective and environmentally friendliness solvent, which is important from the point of view of green chemistry. The present work has also several benefits like avoiding tedious work-up procedures, no need of special experimental setup, more efficiency, reusability, and recyclability of catalyst.