Sohal, Harvinder Singh, et al. “Catalyst Free, One-Pot, Facile Synthesis of Novel Pyrazolo-1,4-Dihydropyridine Derivative Form Pyranopyrazoles”. European Journal of Chemistry, vol. 5, no. 2, June 2014, pp. 227-32, doi:10.5155/eurjchem.5.2.227-232.967.