Sulfonated rice husk ash (RHA-SO3H) as a highly efficient and reusable catalyst for the synthesis of some bis-heterocyclic compounds

Sulfonated rice husk ash (RHA-SO3H), a newly reported solid acid catalyst, was efficiently used for the synthesis of 4,4 '-(arylmethylene)-bis-(3-methyl-1-phenyl-1H-pyrazol-5-ols), 3,3 '-(arylmethylene)-bis-(4-hydroxycoumarins) and bis(indolyl)methanes. The procedure gave the products in excellent yields within very short reaction times under mild and green conditions. Also this catalyst can be reused several times without appreciable loss of its catalytic activity.