A. El-Essawy, Farag, and Safaa I.M. Rady. “Synthesis of Some N-Alkylated and 1,2,4-Triazole, 1,3,4-Oxa-, Thiadiazoles Containing 1H-Pyrazolo[3,4-b]pyridine Derivatives”. Asian Journal of Chemistry, vol. 23, no. 6, Mar. 2011, pp. 2461-7, https://asianpubs.org/index.php/ajchem/article/view/10462.