ASHNAGAR, A., and J.M. BRUCE. “Synthesis of Diels-Alder Bis-Adducts of Methoxycarbonyl-1,4-Benzoquinone”. Asian Journal of Chemistry, vol. 22, no. 6, May 2010, pp. 4602-10, https://asianpubs.org/index.php/ajchem/article/view/16817.