A highly efficient green protocol for the preparation of bis-indolylmethanes, bis-2-methylindolylmethanes, bis-1-methylindolylmethanes and 3,3′-diindolyloxindole derivatives from the reaction of indoles with various aldehydes and ketones in the presence of cellulose sulfuric acid under solvent-free conditions is reported. The significant features of this procedure are high yields of the products, mild reaction, solvent-free condition and non-toxicity of the catalyst.
