Studies on the Biginelli reaction: a mild and selective route to 3,4-dihydropyrimidin-2(1H)-ones via enamine intermediates

l-Proline methyl ester hydrochloride was found to be an effective catalyst for assembling (±)-dihydropyrimidinones under mild conditions. Mechanistic insights into the useful selectivity elements of this amine-catalyzed process are also reported.