Advanced Catalyst-Free Pseudo-Six-Component Synthesis of Tetrahydrodipyrazolopyridines in Water by Using Ammonium Carbonate as an Ecofriendly Source of Nitrogen

This work describes an improved environmentally friendly method for the synthesis of tetrahydrodipyrazolopyridines (THDPPs) in water through a catalyst-free pseudo-six-component reaction of alkyl acetoacetates, hydrazine hydrate, and ammonium carbonate with an aldehyde in a mole ratio of 2:2:1:1 at room temperature. The ammonium carbonate serves as a green source of nitrogen for the central 1,4-dihydropyridine ring in the THDPPs. Methyl acetoacetate reacts faster than either ethyl or propyl acetoacetate in this method. The product precipitates during the reaction and is simply collected by filtration. Advantages of this environmentally benign method include no use of an organic solvent, no hazardous waste, rapid clean reactions, and excellent yields of products.