An environmentally benign, simple, efficient, and convenient route is described for the synthesis of novel pyrazolo[1,5-a]pyrimidine derivatives under ultrasound irradiation. Condensation of aminopyrazole 5 with formylated active proton compounds (6, 8, E-G, 12, and 15) furnished pyrazolopyrimidine (7, 9, 10, 13, and 16) in high-to-excellent yields. In comparison with conventional methods, ultrasound irradiation offers several advantages, such as shorter reaction time, higher yields, milder conditions, and environmental friendliness. The reaction is clean with excellent yields and reduces the use of solvents. X-ray crystallographic study of compound 7c confirmed the regioselectivity of the reaction. The antibacterial profile of the newly synthesized compounds was evaluated by cup and saucer method.
A series of antipyrinyl-pyrazolo[1,5-a]pyrimidines have been synthesized by reactions of aminopyrazole (4) with various formylated active proton compounds in the presence of KHSO4 (aqueous media), under ultrasound irradiation. The structures of the compounds have been established with the help of spectral and analytical data. N-(1,5-Dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)-7-phenylpyrazolo[1,5-a]pyrimidine-3-carboxamide (6a) was further subjected to X-ray crystallographic studies to avoid any ambiguity of the derived structures. Crystal data for compound 6a, C51H46N12O5 (M =907.00 g/mol): triclinic, space group P-1 (no. 2), a = 9.9554(3) Å, b = 14.0875(4) Å, c = 17.4572(4) Å, α = 79.676(2)°, β = 85.283(2)°, γ = 72.647(2)°, V = 2297.97(11) Å3, Z = 2, T = 296.15 K, μ(MoKα) = 0.088 mm-1, Dcalc = 1.311 g/cm3, 29732 reflections measured (4.174° ≤ 2Θ ≤ 57.068°), 10681 unique (Rint = 0.0400, Rsigma = 0.0533) which were used in all calculations. The final R1 was 0.0566 (I > 2σ(I)) and wR2 was 0.1663 (all data). The novel compounds were also screened for their biological activities.
3-Aminopyrazoles required for the synthesis of pyrazolo[1,5-a]pyrimidines were obtained by the reaction of enaminonitriles with hydrazine hydrate. The resulting aminopyrazoles are reacted with formylated acetophenones under reflux at [Formula: see text] assisted by KHSO[Formula: see text] in aqueous media to form regioselectively 3,7-diarylpyrazolo[1,5-a]pyrimidines and 3,6-diarylpyrazolo[1,5-a]pyrimidine-7-amines. X-ray crystallography of selected compounds 5b and 7i further confirmed the regioselective formation of these products.
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