Students work individually. The rea

Students work individually. The reaction is carried out at the 4 mmol level for the aryl aldehyde. Urea (2 equiv), 1,3-dicarbonyl compound (2 equiv), aryl aldehyde (1 equiv), and ytterbium(III) triflate hydrate (0.1 equiv) are dissolved in acetic acid and water solvent (3:1) in a reaction vial containing a magnetic stir bar. An oil bath is heated to 95 °C and the capped vial is kept in the oil bath for 15 min. The reaction mixture is cooled to room temperature; the contents are poured onto ice and the product is precipitated with ice-cold water. The precipitate is collected by vacuum filtration and washed with ice-cold water and toluene under vacuum to remove residual acetic acid; the dihydropyrimidines are white, yellow, or orange solids. Each student obtains an IR spectrum and submits a sample for 1H NMR analysis during the laboratory period. 13C NMR and DEPT data are provided for analysis.