D. S. Kawade, S. N. Deshmukh, J. B. Gujar, and M. S. Shingare, “Tannic Acid an Efficient Catalyst for the Synthesis of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one Derivatives”, Orbital: Electron. J. Chem., vol. 7, no. 2, pp. 155-159, Jun. 2015.