RAGHOTHAM, A., et al. “A Facile Synthesis of 7-Hydroxy-4-Methyl-8-Heteryl-2H-2-Chromenones”. Asian Journal of Chemistry, vol. 20, no. 2, Mar. 2010, pp. 1285-9, https://asianpubs.org/index.php/ajchem/article/view/12539.