Ethyl acetoacetate (Acros Organics), 5-methylthiophene-2-carboxaldehyde (Aldrich), urea (Merck), magnesium bromide (Aldrich).

A mixture of ethyl acetoacetate (2 mmol), 5-methylthiophene-2-carboxaldehyde (2 mmol), urea (3 mmol) and magnesium bromide (0.2 mmol) was heated at 100 ^oC with stirring until the mixture turned to solid mass (45 min). After completion (monitored by TLC), the solid was cooled to room temperature and poured onto crushed ice (20 g) and stirred for 10 min. The crude product was filtered, washed with cold water (2x10 mL) and then recrystallized from ethanol or ethyl acetate/n-hexane to afford white crystals. Yield (494 mg, 88%)

This is an environmentally friendly procedure for the synthesis of dihydropyrimidinones/thiones by using magnesium bromide as an inexpensive and easily avaliable catalyst under solvent-free conditons. This reaction was carried out with ethyl acetoacetate and thiourea, tert-butyl acetoacetate and urea/thiourea and allyl acetoacetate and urea/thiourea to give the corresponding Biginelli products in good yields. The author thanks Çanakkale Onsekiz Mart University (BAP 2008/28) for financial support.

m.p.: 232-234 ^oC, IR-ATR: 3233, 3110, 2971, 1723, 1702, 1650 cm^-1; ¹H-NMR (400MHz, DMSO-d₆): 9.27 (s, 1H, NH), 7.83 (s, 1H, NH), 6.65 (d, 1H, J=3.4 Hz, H_ar), 6.60 (m, 1H, H_ar), 5.31 (d, 1H, J=3.5 Hz, CH), 4.07 (q, 2H, J=7.1 Hz, OCH₂CH₃), 2.36 (s, 3H, CH₃), 2.21 (s, 3H, CH₃), 1.18 (t, 3H, J=7.1 Hz, OCH₂CH₃); ¹³C-NMR (100MHz, DMSO-d₆): 165.5, 152.72, 148.95, 146.67, 138.41, 125.10, 123.69, 100.24, 59.79, 49.91, 18.12, 15.42, 14.64.

H. Salehi, Q. X. Guo, Synth. Commun. 2004, 34, 171-179.

H. Salehi, Q.R.Li, Q. X. Guo, Chin. J. Chem. Phys. 2006, 19, 84-88.