Davoodnia, A., et al. “Montmorillonite K10 As an Efficient and Reusable Catalyst for the Synthesis of Substituted Pyrazolo[3,4-d]pyrimidin-4-Ones Under Solvent-Free Conditions”. Asian Journal of Chemistry, vol. 24, no. 5, Jan. 2012, pp. 2195-8, https://asianpubs.org/index.php/ajchem/article/view/8978.