Design of fused systems based on σH-adducts of 6-nitro-1,2,4-triazolo[1,5-a]pyrimidine with π-excessive heteroaromatic compounds

Dihydroazolopyrimidines: Past, Present and Perspectives in Synthesis, Green Chemistry and Drug Discovery

“…[23,55] Heteroaromatization of dihydrocycles can also be observed as disproportionation process (reaction p, Scheme 9) or together with the reduction of other molecular moieties or substituents (reaction q). [90][91][92] The action of tosylazide on 4,5-dimethyl-7-phenyl-4,7dihydro-1,2,4-triazolopyrimidine occurs by cycloaddition with prior formation of the 1,2,3-triazoline cycle; further elimination of the nitrogen molecule occurs by rearrangement of the carbon skeleton of the molecule (reaction r, Scheme 10). [93] Thus, in addition to the characteristic reactions of dihydroazines, dihydroazolopyrimidine derivatives also have the ability to undergo interactions more typical for heteroaromatic compounds.…”

Synthesis of Condensed Heterocycles, Containing Partially Saturated Pyrimidine Nuclei, from Aromatic Pyrimidine Derivatives

“…The reaction of 53 and 54 with some π‐excessive aromatic and heterocyclic compounds to proceedes smoothly at reflux temperature giving the corresponding σ‐adducts 56 and 57 . These fused dihydropyrimidine derivatives 55 – 57 are formed in high yields as stable crystalline substances.…”

Oxidative Aromatization of 4,7-Dihydro-6-nitroazolo[1,5-a]pyrimidines: Synthetic Possibilities and Limitations, Mechanism of Destruction, and the Theoretical and Experimental Substantiation

“…From the point of view of biological activity, these compounds exhibit antiviral [ 31 , 32 ], antiseptic [ 33 , 34 ], antioxidant [ 35 , 36 ], antitumor [ 37 ], and antiglycation activity [ 38 ]. From a synthetic point of view, the nitro groups are not only a quasi-form of the amino groups for creating azoloannelated purines [ 39 , 40 , 41 ], but they also, for example, open pathways for the modification of molecules by various nucleophiles [ 42 , 43 ]. Some useful azolo[1,5-a]pyrimidines are shown in Figure 1 .…”

“…Previously we discovered the multicomponent reaction between aminoazoles, aromatic aldehydes, and 1-morpholino-2-nitroalkenes, which proceeds through different mechanisms depending on catalysis with Lewis [ 44 ] or Brønsted acids [ 45 ] ( Scheme 1 a,b). Formed that way, 4,7-dihydro-6-nitroazolo[1,5-a]pyrimidines have been obtained by the condensation of corresponding azoles with sodium salts of malonic dialdehyde [ 46 ] and the subsequent nucleophilic addition of π-extended (hetero)aromatic systems [ 43 , 47 , 48 ] ( Scheme 1 c). However, that approach has the following few disadvantages: a two-step synthesis procedure, an exclusively nucleophilic variant of structural modifications, and the limitation of possible modification positions.…”