An Expeditious Synthesis of Tetrahydro-1,2,4-triazolo[5,1-b]quinazolin-8(4H)-ones and Dihydro-1,2,4-triazolo[1,5-a]pyrimidines

Synthesis and N-alkylation of diethyl 4,7-dihydroazolo[1,5-a]pyrimidin-5,6-dicarboxylates

“…It is interesting that unlike the above-mentioned alkylation of 6-acetyl-5-methyl-7-phenyl-4,5-dihydro [1,2,4]triazolopyrimidine [8] the process in this case occurred selectively (which was favoured by 1 H NMR-spectra of the products obtained). In contrast to the 1 H NMR spectrum of the initial compounds 5, the signal of NH-protons is absent in a low field, but the signal of NCH 3 -group is present.…”

“…triazolo [1,5-a]pyrimidin -5,6-dicarboxylate) it has been found that alkylation of 4,7-dihydro [1,2,4]azolo [1,5-a]pyrimidin -5,6- [1,2,4] triazolo [1,5-a]pyrimidines are the promising objects for studying benzyl C(7)-functionalization of 4,7-dihydroazolo [1,5-a] [1,2,4] triazolo-and tetrazolo [1,5- [1,2,4]triazolo-and tetrazolo [1,5-a] [1,2,4]триазоло [1,5-a] Previously we reported about the synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives of type 1 and 2 (Fig. 1).…”

“…Besides, for compound 5a the signal of C(2)-proton at 7.70 ppm (separately from aromatic protons signals) is observed. It is also worth noting that the signal of one of the CH 2 -groups (3.82-4.07 ppm for compound 5а) like the spectrum of 6-acetyl-4-ethyl-5-methyl-7-phenyl-4,5-dihydro [1,2,4]triazolopyrimidine [8] is a multiplet, and it indicates its diastereotopism. Diastereotopism of the second CH 2 -group does not reveal obviously because of the presence of flexible bonds between the ethoxycarbonyl group and the dihydrocycle, which contains a chiral centre, as well as due to a rather long distance from the CH 2 -group to the chiral centre.…”

“…These substances (especially N-alkylated compounds 1b, 2f,g) are the promising objects for C(4)-functionalization of the 3,4-dihydropyrimidin-2(1H)-one cycle and contain the activated С=С-bond. Searching for the similar structures, which are more suitable for introduction of substituents in the benzyl position than compounds 1 and 2, we drew attention to the derivatives of 4,7-dihydroazolo[1,5-a] pyrimidines of type 3 [3][4][5][6][7]. The absolute advantage of these compounds is high stability of the triazole cycle toward the action of nucleophilic reagents.…”

“…In conclusion, in this report we have 4 as an internal standard, chemical shifts are given in ppm, coupling constants are given in Hz. IR spectra were recorded in KBr pellets using a Specord IR-75 spectrometer.…”