Pyrazolone scaffold

The pyrazolone scaffold is the basis of the analgesic anti-inflammatorief phenylbutazone and amtnopyrtne. 

An interesting entry to functionalized dihydropyrans has been intensively studied by Tietze in the 1990s using a three-component domino-Knoevenagel Hetero-Diels-Alder sequence. The overall transformation involves the transient formation of an activated heterodienophile by condensation of simple aldehydes with 1,3-dicarbonyls such as barbituric acids [127], Meldrum s acid [128], or activated carbonyls. In situ cycloaddition with electron-rich alkenes furnished the expected functionalized dihydropyrans. Two recent examples concern the reactivity of 1,4-benzoquinones and pyrazolones as 1,3-dicarbonyl equivalents under microwave irradiation. In the first case, a new three-component catalyst-free efficient one-pot transformation was proposed for the synthesis of pyrano-1,4-benzoquinone scaffolds [129]. In this synthetic method, 2,5-dihydroxy-3-undecyl-1,4-benzoquinone, paraformaldehyde, and alkenes were suspended in ethanol and placed under microwave irradiations to lead regioselectively the corresponding pyrano-l,4-benzoquinone derivatives (Scheme 38). The total regioselectivity was... 

Cobalt-doped ZnS-NPs-catalyzed novel strategy has been developed to generate a diverse array of pyrazolones (with exeellent regioseleetivity) representing a privileged medicinal scaffold using IR irradiation as the heating mode [38]. The proposed... 

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