Kaping, Shunan, et al. “A Three Step One-Pot Regioselective Synthesis of Highly Substituted pyrazolo[1,5-a]pyrimidines Assisted by KHSO4 in Aqueous Media under Ultrasound Irradiation”. European Journal of Chemistry, vol. 11, no. 3, Sept. 2020, pp. 179-86, doi:10.5155/eurjchem.11.3.179-186.1977.