Innovative Green Synthesis of 4-Aryl-Pyrazolo[5,6]Pyrano[2,3-<i>d</i>]Pyrimidines under Catalyst-Free Conditions

<p>A clean, cost-effective and practical approach has been described for the convenient synthesis of a library of 4-aryl-pyrazolo[5,6]pyrano[2,3-<i>d</i>]pyrimidines starting from a four-component condensation of ethyl acetoacetate, hydrazine hydrate, aromatic aldehydes, and barbituric/thiobarbituric acid in catalyst-free aqueous ethanol system. The reactions were assisted by water, there by leading to the development of ‘water chemistry’ providing the products in good yields in shorter reaction times. Environmental benignity, neutral reaction conditions, wide range of functional group tolerance, facile experimental and work-up procedures are the prominent features of this greener protocol.</p>