OICC Press Iranian Journal of Catalysis 2345-4865 3 3 2024 02 03 Cellulose sulfuric acid: an efficient biopolymer-based catalyst for the synthesis of 5H-dibenzo[b,i]xanthene-tetraones and spiro[dibenzo[b,i]xanthene-13,3′-indoline]-pentaones under solvent free conditions EN Seyyedeh Cobra Azimi Young Researchers and Elites Club, Rasht Branch, Islamic Azad University, Rasht, Iran. Hassan Kefayati Department of Chemistry, Rasht Branch, Islamic Azad University, Rasht, Iran. 0000-0002-0818-054X Journal Article 2024 02 03 A practical and green method for the synthesis of 5H-dibenzo[b,i]xanthene-tetraones and spiro[dibenzo[b,i]xanthene-13,3'-indoline]-pentaones by the condensation of 2-hydroxynaphthalene-1,4-dione with aldehydes or isatins, respectively, in the presence of a catalytic amount of cellulose sulfuric acid (CSA) under solvent-free conditions at 100 °C is described. The significant features of this procedure are high yields of the products, simple work-up, solvent-free conditions, operational simplicity and non-toxicity of the catalyst. Moreover, cellulose sulfuric acid is successfully reused for four cycles without significant loss of activity.