Ramazani, Ali, et al. “Silica Gel Powder Catalyzed Stereoselective Conversion of 2-(2-Acetylphenoxy)-3- (triphenylphosphoranylidene)- Butanedioates to Dialkyl (Z)-2-(2-Acetylphenoxy)- 2- Butenedioates in Solvent-Free Conditions”. Asian Journal of Chemistry, vol. 18, no. 1, Mar. 2010, pp. 695-7, https://asianpubs.org/index.php/ajchem/article/view/21429.