A green and eco-friendly method for the synthesis of xanthene derivatives using cellulose sulfuric acid under solvent-free conditions

A green and convenient method for the synthesis of 14-aryl-14H-dibenzo[a,i]xanthene-8,13-diones and spiro[dibenzo[a,i]-xanthene-14,3'-indoline]-2',8,13-triones in the presence of a catalytic amount of cellulose sulfuric acid (CSA) as an efficient biopolymer-based catalyst under solvent-free conditions at 100 °C is described. The condensation reactions of β-naphtol, 2-hydroxynaphthalene-1,4-dione with aldehydes or isatins to afford the corresponding xanthenes in good to excellent yields. To the best of our knowledge, it is the first example of a multicomponent reaction to the synthesis of these compounds using cellulose sulfuric acid. The present approach offers several advantages such as shorter reaction times, simple work-up, excellent yields, non-toxicity of the catalyst, and solvent-free conditions. Moreover, cellulose sulfuric acid is successfully reused for four cycles without significant less of activity.