Dung, Pham, and Tai Nguyen. “Synthesis of Pyrano[3,2-C]quinoline Derivatives Using Catalyst Prepared from L-Proline and P-Toluenesulfonic Acid”. Science and Technology Development Journal - Natural Sciences 5, no. 3 (May 11, 2021): 1275-1283. Accessed June 20, 2021. http://stdjns.scienceandtechnology.com.vn/index.php/stdjns/article/view/1008.