The production of the corresponding
dihydropyrimidinone was increased with a larger
urea from 2 to 2.5 mol%. The desired product was obtained in
90% yield in the presence of 2.5 mmol of urea after 2 h, while
only 67% yield was achieved by 2 mmol of urea after 5 h. A
further increase in urea concentration only reduced the time
(1.2 h) needed to reach the maximum conversion of 73%–84%
(Fig. 2).