Direct (het)arylation of [1,2,4]triazolo[1,5- a ]pyrimidines: Both eliminative and oxidative pathways

Ethynylation of [1,2,4]Triazolo[1,5‐a]pyrimidinesUsing Substituted Ethynylmagnesium Bromides

“…Considering our previous success of the addition of Grignard reagents to TAPs systems, [16] we decided to explore similar reaction with magnesium salts of mono-substituted acetylenes. Based on the 1 H and 13 C NMR spectra of compounds 3 and 4, the most electron-deficient position in both cases is C-7, therefore, a more preferable target for the attack of the nucteophile than the C-5 position of TAP.…”

“…In our previous work, [16] we used oxygen as a aromatizing agent, introducing it into the reaction after the formation of Nmagnesium salts of sigma adducts. This technique did not allow achieving high yields due to the formation of many oxidation by-products.…”

Recent Advances in Direct C–H Functionalization of Pyrimidines

“…The use of Grignard reagents for the direct nucleophilic C-H functionalization of 5-bromopyrimidine and 6-bromo [1,2,4]triazolo[1,5-a]pyrimidine has been investigated. 106,107 A new method to prepare 4-substituted 5-bromopyrimidines 62 in poor to good yields was described in a patent. 106 The one-pot synthetic protocol involves the reaction of 5-bromopyrimidine 59 with the Grignard reagents 60 under an inert gas atmosphere at 0-5 °C and gives 4-substituted 5-bromo-3,4-dihydropyrimidine 61 as an intermediate; oxidative dehydrogenation of 61 in an acidic or alkaline oxidation system afforded 4-substituted 5-bromopyrimidines 62 (Scheme 32).…”

“…The direct (hetero)arylation of [1,2,4]triazolo [1,5-a]pyrimidine through the nucleophilic C-H functionalization of C7 and C5 was reported in 2017. 107 The regioselective addition of a (hetero)arylmagnesium bromide to C7 of 6-bromo [1,2,4] Girke 108 reported that pyrimidine, quinazoline, and purine derivatives 68 activated by trifluoroacetic acid react with a wide variety of aromatic compounds, such as phenols, pyrroles, indoles, thiophenes, and some polycyclic aromatic hydrocarbons, to form rather stable 4-(hetero)arylsubstituted 3,4-dihydropyrimidinium salts 70. These 4-(hetero)aryl-substituted 3,4-dihydro-1,3-diazines 70 were oxidized by treatment with a twofold excess of K 3 Fe(CN) 6 in 33% aqueous KOH solution (Scheme 34).…”

Synthesis, photophysical and redox properties of the 2,5,7-tri(het)aryl-[1,2,4]triazolo[1,5-a]pyrimidines

“…Indeed, substituted TAPs show good fluorescence features, especially in the blue region of spectra. 11 Since there is still a great demand for blue emitting materials with high efficiency, 12,13 TAPs seem to be an attractive object for the further research.…”