This study aims to use a new medicinal porous plant having a high content of silica known as horsetail and horsetail ash for the first time as novel, efficient, and environmentally friendly natural mild catalysts. The structure of these catalysts was characterized by different techniques such as FT-IR, XRF, SEM–EDS, N2 adsorption–desorption, XRD, and ICP analysis. The results obtained from the analysis revealed that both horsetail and horsetail ash could act as a solid acid catalyst. In addition, a further detailed analysis illustrated that they have a different surface area, porosity, and crystalline structure which can affect their catalytic activities. The synthesis of 2-amino-4H-chromene derivatives was performed via a one-pot threecomponent condensation of dimedone, malononitrile, and various aromatic aldehydes to compare their catalytic activities under solvent-free conditions. Due to its high porosity and high surface area, horsetail ash yields better results compared to the horsetail itself. FT-IR, mass, 1H-NMR, and 13C-NMR spectroscopies were used to identify the synthesized compounds in this study. An important advantage of this method is the use of these effective natural catalytic systems with characteristics such as low cost, mild reaction conditions, nontoxicity, and reusability which resulted in corresponding products in high to excellent yields and proper reaction times.

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