Heterocycl. Commun., Vol. 18(2), pp. 67–70, 2012 • Copyright © by Walter de Gruyter • Berlin • Boston. DOI 10.1515/hc-2011-0060 Synthesis of novel benzo[ f ]chromene compounds catalyzed by ionic liquid Hossein Eshghi 1 , Gholam Hossein Zohuri 1 , Reza Sandaroos 2 and Saman Damavandi 3, * 1 Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran 2 Department of Chemistry, Faculty of Science, Birjand University, Birjand, Iran 3 Department of Chemistry, Sarvestan Branch, Islamic Azad University, Sarvestan, Iran * Corresponding author e-mail: Saman_Damavandi@yahoo.com Abstract A facile method for the synthesis of benzo[ f]chromene deriv- atives is reported. The procedure involves a novel three-com- ponent reaction of 1-naphthol or 2-naphthol, acetophenone derivatives and triethyl orthobenzoate in the presence of sil- ica supported ionic liquid [pmim]HSO 4 SiO2 [silica supported 1-methyl-3-(triethoxysilylpropyl)imidazolium hydrogensul- fate] as an efficient catalyst. Keywords: benzo[f]chromene; ionic liquid; one-pot reaction. Introduction Currently, one of the major challenges of modern drug dis- covery is the design of highly efficient chemical reaction sequences providing a maximum of structural diversity using a minimum number of synthetic steps to assemble compounds with interesting properties (Dömling, 2002). Recently, multi- component reactions (MCRs) have emerged as a highly valu- able synthetic tool in the realm of modern drug discovery. The atom economical and convergent character, the simplic- ity of a one-pot procedure, the possible structural variations, the accessible complexity of the molecules, as well as the very large number of accessible compounds are among the described advantages of MCRs (Trost, 1995). Recently, ionic liquids have become a powerful alterna- tive to conventional molecular organic solvents due to their particular properties, such as undetectable vapor pressure and the ability to dissolve many organic and inorganic substances (Wasserscheid and Welton, 2007). In addition, the ionic liq- uids are readily recycled and tunable to specific chemical tasks. One type is Brønsted acidic task-specific ionic liquids. Among these ionic liquids possessing HSO 4 as a counteran- ion finds a broad application in organic synthesis, acting as both a solvent and a catalyst. Recently, immobilization processes involving acidic ionic liquids on solid supports have been designed (Du et al., 2006; Gupta et al., 2007; Wang et al., 2008). The heterogenization of catalysts and reagents can offer important advantages in handling, separation and reuse procedures. Immobilized acidic ionic liquids have been used as novel solid catalysts for a wide spectrum of reactions (Fischer et al., 1999; Qiao et al., 2006; Sugimura et al., 2007). Chromenes and fused chromenes are biologically active compounds and they are used as cosmetics and pigments (Hafez et al., 1987; Ellis et al., 1997), spasmolytic, diuretic, anticoagu- lant, antianaphylactic (Triggle, 2003; Poupaert et al., 2005), antibacterial (Kidwai et al., 2005), anticancer agents (Mohr et al., 1975), and as potent apoptosis inducers (Gao et al., 2010). Recently, many studies have been devoted to the synthesis of benzo[ f]chromene compounds by developing and modification of synthetic methods. Claisen rearrangement of alkynyl aryl ethers from propargylic alcohols and naphthols under acid catalysis to synthesize 2 H-1-benzopyran derivatives has been reported (Xu et al., 2009). In addition, several catalysts have been utilized for the synthesis of 2-amino-4 H-chromenes such as cetyltrimeth- ylammonium chloride (Ballini et al., 2000), cetyltrimethylammo- nium bromide under ultrasound irradiation (Jin et al., 2004), KF/ Al 2 O 3 (Wang et al., 2004), TiCl 4 (Sunil et al., 2006), triethylamine (Shestopalov et al., 2002), basic ionic liquids (Gong et al., 2008), iodine/K 2 CO 3 (Ren and Cai, 2008), and DABCO (Balalaie et al., 2008). However, synthesis of 1-ethoxy-3-(4-aryl)-1-phenyl-1- H-benzo[ f]chromene has never been reported up to now. In the course of our ongoing research for the efficient and convenient synthesis of a variety of heterocyclic compounds (Damavandi, 2011; Damavandi and Sandaroos, 2011a; Damavandi and Sandaroos, 2011b), we developed an efficient synthetic proce- dure for the synthesis of a series of benzo[ f]chromenes by one-pot condensation of 2-naphthol or 1-naphthol, acetophenone deriva- tives and triethyl orthobenzoate catalyzed by silica supported ionic liquid of [pmim]HSO 4 SiO 2 [silica supported 1-methyl-3- (triethoxysilylpropyl)imidazolium hydrogensulfate] (Scheme 1). Results and discussion Attempts have been made by many research groups to pre- pare supported catalysts in the area of transition metal cat- alyst mediated various organic reactions (De et al., 2002; Rechavi and Lemaire, 2002). In the present study, [pmim] HSO 4 SiO2 (Scheme 1) was prepared based on a published report (Chrobok et al., 2009). Initial experiments were performed with 2-naphthol, acetophenone and triethyl orthobenzoate as the model sub- strates. When 2-naphthol (1 mmol) was treated with aceto- phenone (1 mmol) and triethyl orthobenzoate (1 mmol) in the