Silica-Bonded S-Sulfonic Acid as Recyclable Catalyst for the Synthesis of 1,8-Dioxo-decahydroacridines and 1,8-Dioxo-octahydroxanthenes Khodabakhsh Niknam,* Farhad Panahi, Dariush Saberi, and Molki Mohagheghnejad Faculty of Sciences, Department of Chemistry, Persian Gulf University, Bushehr 75169, Iran *E-mail: khniknam@gmail.com Received July 7, 2009 DOI 10.1002/jhet.303 Published online 23 February 2010 in Wiley InterScience (www.interscience.wiley.com). Silica-bonded S-sulfonic acid (SBSSA) has been found to be an efficient catalyst for the synthesis of 1,8-dioxo-decahydroacridines and 1,8-dioxo-octahydroxanthenes in excellent yields. The former have been synthesized from aromatic aldehydes, amines, and 5,5-dimethyl-1,3-cyclohexanedione, whereas the latter from this mixture without amines. The method is an easy access to functionalized acridine and xanthene derivatives. The catalyst can be reused. J. Heterocyclic Chem., 47, 292 (2010). INTRODUCTION The development of heterogeneous catalysts for fine chemical synthesis has become a major area of research. The potential advantages of these materials over homo- geneous systems (simplified recovery and reusability, the potential for incorporation in continuous reactors and micro reactors) can lead to novel and environmen- tally benign chemical procedures for academia and industry [1]. From this viewpoint, catalytic reactions lead to valuable processes, because the use of stoichio- metric reagents that are often toxic poses inherent limi- tations from both an economical and an environmental viewpoint and in specific relation to product purification and waste management [2]. It is clear that green chemis- try not only requires the use of environmentally benign reagents and solvents but also it is very crucial to recover and reuse the catalyst. One way to overcome the problem of recyclability of the traditional acid cata- lyst is to chemically anchor their reactive center onto a large surface area inorganic solid carrier to create new organic–inorganic hybrid catalyst [3]. In these types of solids, the reactive centers are highly mobile similar to homogeneous catalysts and at the same time these spe- cies have the advantage of being recyclable in the same fashion as heterogeneous catalysts. In view of this, sev- eral types of solid sulfonic acid functionalized silica (both amorphous and ordered) have been synthesized and applied as an alternative to traditional sulfonic acid resins and homogeneous acids in catalyzing chemical transformations [4,5]. Application of solid acids in or- ganic transformation has an important role, because these species have many advantages, such as, simplicity in handling, decreased reactor and plant corrosion prob- lems, and more environmentally safe disposal [4–10]. 1,8-Dioxo-9-aryl-10-aryl-decahydroacridines and their derivatives are polyfunctionalized 1,4-dihydropyridine derivatives. In recent years, 1,4-dihydropyridines and their derivatives have attracted strong interest for the treatment of cardiovascular diseases, such as, angina pectoris [11] and hypertension [12]. Acridine derivatives have been used to synthesize labeled conjugates with medicinals, peptides, proteins, and nucleic acids [13–15] that exhibit antitumor and DNA-binding properties. Multicomponent reactions (MCRs) constitute, an V C 2010 HeteroCorporation 292 Vol 47