Chao, S.; Lu, G.; Wu, L. Amberlyst-15 Catalyzed Synthesis of 12-Aryl-12H-benzo[i][1,3]-dioxolo[4,5-b]xanthene- 6,11-Diones and 14-Aryl-14H-dibenzo[a,i]xanthene-8,13-Diones under Solvent-Free Condition. ajc 2011, 23, 3865-3869.