Reactions of 4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidines with α,β-unsaturated carbonyl compounds

The reaction of 5,7-diphenyl-4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidine (1) with α,β-unsaturated carbonyl compounds 2a-f led to the formation of the alkylated heterocycles 3a-f (Figure 1). However, the reaction of 5-methyl-7-phenyl-4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidine (5) with 2a-c yielded under the same conditions the triazolo[5,1-b]quinazolines 6a-c (Figure 3). In this case, the alkylation is followed by a cyclocondensation. The structure elucidation of the products is based on ir, ms, 1H and 13C nmr measurements and on an X-ray diffraction study.