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Chapter 1
Synthesis of functionalized pyrimidines
Ultrasound assisted synthesis
Ultrasound as a green synthetic approach has gradually been used in organic
synthesis over the last three decades. Compared with the traditional methods, it is
more convenient, easier to be controlled and consumes less power. With the use of
ultrasound irradiation, a large number of organic reactions can be carried out in milder
conditions with shorter reaction time and higher product yields. 49 Ultrasound
irradiated and amidosulfonicacid (NH 2 SO 3 H) catalyzed synthesis of 3,4-
dihydropyrimidi-2-(1H)ones have been reported by Li J. T. and co-workers 50 using
aldehydes, β-ketoester and urea.
Liu C. et al. 51 have synthesized a novel series of 4-substituted pyrazolyl-3,4-
dihydropyrimidin-2(1H)-thiones under ultrasound irradiation using magnesium
perchlorate [Mg(ClO 4 ) 2 ] as catalyst (Figure-21), by the condensation of 5-
chloro/phenoxyl-3-methyl-1-phenyl-4-formylpyrazole, 1,3-dicarbonyl compound and
urea or thiourea in moderate yields. The catalyst exhibited remarkable reactivity and
can be recycled.
Figure-21
Sonication of aromatic aldehydes, urea and ethyl acetoacetate in presence of
solvent (ethanol) or solvent-less dry media (bentonite clay) by supporting-zirconium
chloride (ZrCl 4 ) as catalyst at 35 kHz gives 6-methyl-4-substitutedphenyl-2-oxo-
1,2,3,4-tetrahydropyrimidine-5-carboxylic acid ethyl esters proficiently in high yields,
which reported by Harish Kumar et al. (Figure 22). 52
Figure-22
Department of Chemistry, Saurashtra University, Rajkot-360005 12