Cyclocondensation of 3(5)‐alkylamino‐ and 3(5‐arylaminopyrazoles 1a‐c and 1d‐e with formaldehyde and primary amines affords novel tetrahydropyrazolo[3,4‐d]pyrimidines 2 and tetrahydropyrazolo[1,5‐a]triazine derivatives 3 respectivley in good yields.

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 facile one-pot synthesis of 5-benzoyl-6-methylthio-1,2,3,4-tetrahydropyrimidines in good yields is reported.

1-(Aralkyl/aryl)-3-(alkyl/aralkyl)-5-aroyl-1,2,3,4-tetrahydropyrimidines (2a-c) have been synthesized by dethiomethylation of 5-aroyl-6-methylthio-1,2,3,4-tetrahydropyrimidines (1 a -c). An alternative one-pot synthetic strategy has been developed for the title compounds 2a-t by the reaction of enaminones 3 with primary amine and formaldehyde in refluxing methanol in good yields.

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