Fang, Li-Zhen, et al. “Facile Preparation of the Synthon of 7-Ethyl-8-oxabicyclo[4.3.0]nonane-2,9-Dione”. Asian Journal of Chemistry, vol. 23, no. 7, Mar. 2011, pp. 2919-21, https://asianpubs.org/index.php/ajchem/article/view/10527.