The superiority of the present method over other reported
protocols can be seen by comparing the present results with
those reported previously (Table 5). The three component
condensation of urea, acetoacetate, and 4-nitrobenzaldehyde to
ethyl-6-methyl-4-(4-nitrophenyl)-2-oxo-1,2,3,4-tetrahydropyri
midine-5-carboxylate was selected as a model reaction and the
comparison was made in terms of the catalyst, reaction time,
and percentage yield. Although some of the other catalysts
gave marginally higher conversions, however, they required
long reaction time and a higher amount of catalyst. The present
method used a small amount (5 mol%) of a cheap and environmentally
friendly catalyst under solvent-free condition and
required a relatively short reaction time.