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.