Acetic aldehyde in multicomponent synthesis of azolopyrimidine derivatives in water

Three-component reaction of 3-amino-1H-1,2,4-triazole or 5-amino-2H-1,2,3-triazole derivatives, acetaldehyde, and 1,3-dicarbonyl compounds (acetylacetone or -keto esters) in water under microwave irradiation leads to regioselective formation of 4,7-dihydro[1,2,4]-triazolo- and 4,7-dihydro[1,2,3]triazolo[1,5-a]pyrimidines. Using ethyl 4,4,4-trifluoro-3-oxobutanoate as 1,3-dicarbonyl compound under the same conditions allows to obtain the corresponding 5-hydroxy-4,5,6,7-tetrahydro derivatives, which fail to dehydrate in the reaction medium.