A simple and efficient method for synthesis of 5,7-disubstituted pyrazolo[1,5-a]pyrimidines is reported. The synthetic route involved first a one-pot two-step synthesis of 7-substituted pyrazolo[1,5-a]pyrimidin-5-ones from the reaction of 3-aminopyrazole 1 with activated alkynes. These compounds were used as key intermediates to access, with excellent yields, a library of new 5,7-disubstituted pyrazolo[1,5-a]pyrimidines, which are known for their wide range of biological activities, through C–O bond activation with PyBroP (bromotripyrrolidino-phosphonium hexafluorophosphate) as an activator reagent.