Background: Bis(indolyl)methane, indole and their derivatives are known as vital intermediates
in the pharmaceutical chemistry and organic synthesis which exhibits a range of physiological
properties. Bis(indolyl)methanes are found in cruciferous plants and are well known to promote beneficial
estrogen metabolism and induce apoptosis in human cancer cells. Bis(indolyl)methanes have received
much attention in recent years. A major source of waste in the (fine) chemicals industry is derived
from the widespread use of liquid mineral acids (HF, H2SO4) and a variety of Lewis acids. They
cannot be easily recycled and generally end up as waste containing large amounts of inorganic salts.
Their widespread replacement by recyclable solid acids such as malic acid, tartaric acid and malonic
acid etc., which are naturally occurring, would afford a dramatic reduction in waste. Thus there is need
to find out green protocols for the synthesis of bioactive molecules.
Objective: To develop green protocol for the synthesis of bisindolylmethane derivatives.
Methods: Bisindolylmethane derivatives were synthesized in 85-95 % by using ultrasonication technique
in presence of malic acid as an organocatalyst in water as a green solvent at ambient reaction
Results: We have demonstrated that malic acid can be used as a benign organocatalyst for organic
transformations with high efficacy and excellent reusability.
Conclusion: In conclusion, we have developed ultrasonically assisted malic acid catalyzed metal free
green protocol for the bis(indolyl)methanes under homogenous conditions. The notable advantages of
this method are the use of water as a green solvent, efficient eco-friendly and inexpensive catalyst,
ambient temperature and high reusability of the catalyst. Therefore, this protocol can be a promising
alternative to the use of Lewis and mineral acid catalysed organic reactions. Further studies of exploiting
the efficiency of naturally occurring acids as a green catalyst in synthesis of various heterocyclic
compounds are in progress.