Synthesis, effect of substituents on the regiochemistry and equilibrium studies of tetrazolo[1,5-a]pyrimidine/2-azidopyrimidines

An efficient synthesis methodology for a series of tetrazolo[l,5-a]pyrimidines substituted at the 5-and 7-positions from the cyclo-condensation reaction [CCC + NCN] was developed. The NCN corresponds to 5-aminotetrazole and CCC to beta-enaminone. Two distinct products were observed in accordance with the beta-enaminone substituent. When observed in solution, the compounds can be divided into two groups: (a) precursor compounds with R = CF(3)or CCl3, which leads to tetrazolo[l,5-a]pyrimidines in high regioselectivity with R at the 7-position of the heterocyclic ring; and (b) precursor compounds with R = aryl or methyl, which leads to a mixture of compounds, tetrazolo[l,5-a] pyrimidines (R in the 5-position of the ring) and 2-azidopyrimidines (R in the 4-position of the ring), which was attributed to an equilibrium of azide-tetrazole. In the solid state, all compounds were found as 2-azidopyrimidines. The regiochemistry of the reaction and the stability of the products are discussed on the basis of the data obtained by density functional theory (DFT) for energetic and molecular orbital (MO) calculations.