First, in situ generated Mannitol-Boron or Sorbitol-Boron chelate complex as a novel, recyclable catalyst for the highly efficient synthesis of bis(indolyl)methanes, tris(indolyl)methanes and diindolyl (carbazolyl)methanes.

Abstract The first report on in situ generated Mannitol-Boron or Sorbitol-boron chelate complex, as a novel, recyclable homogenous, eco-benign catalyst for the liquid phase electrophilic substitution reactions of indoles with aromatic aldehydes or indole aldehydes or carbazole aldehydes to afford the corresponding bis(indolyl)methanes or tris(indolyl)methanes or di(indolyl) carbazolyl methanes in ethanol or aqueous ethanol at ambient temperature in good to excellent yields. This methodology is mild, highly efficient using minor quantities of catalyst with no side products and a very simple work-up procedure. The effect of solvent, the effect of substituents and the influence of mole ratio are also investigated. The addition of mannitol or sorbital to boric acid in excess formed mainly a 2, 2-di-borate ester which can be effectively removed from reaction waste water (> 97%) by subjecting the reaction waste water to reverse osmosis.