Davoodnia, A., et al. “Microwave Synthesis of New Pyrazolo[3,4-d]pyrimidin-4-Ones in Solvent-Free Condition”. Asian Journal of Chemistry, vol. 23, no. 8, May 2011, pp. 3683-5, https://asianpubs.org/index.php/ajchem/article/view/10668.