High Surface Area MgO as a Highly Effective Heterogeneous Base Catalyst for Three-Component Synthesis of Tetrahydrobenzopyran and 3,4-Dihydropyrano[c]chromene Derivatives in Aqueous Media Mohammad Seifi Æ Hassan Sheibani Received: 20 February 2008 / Accepted: 24 July 2008 / Published online: 4 November 2008 Ó Springer Science+Business Media, LLC 2008 Abstract Magnesium oxide (MgO) as a highly effective heterogeneous base catalyst effectively catalyzes the three component reaction of aryl aldehydes, malononitrile and a-hydroxy or a-amino activated C–H acids such as 1,3- cyclohexanedione, dimedone, 4-hydroxy-6-methylpyrone, 4-hydroxycoumarin, 1,3-dimethylbarbituric acid and 1,3- dimethyl-6-amino uracil to the formation of the corre- sponding pyran annulated heterocyclic systems. The catalyst is inexpensive and easily obtained, stable and storable, easily recycled and reused for several cycles with consistent activity. Keywords Magnesium oxide (MgO) Á Malononitrile Á Tetrahydrobenzopyran Á Three-component reaction 1 Introduction In recent years, 4H-pyrans and its derivatives have attracted strong interest due to their useful biological and pharmaco- logical properties, such as anticoagulant, spasmolytic, anticancer, antianaphylactin agents [1]. Some 2-amino-4H- pyrans can be employed as photoactive materials [2]. Fur- thermore, substituted 4H-pyrans also constitute a structural unit of a series of natural products [3]. Considering the importance of these compounds, many methods for the synthesis of tetrahydro-4H-benzo-[b]-pyran derivatives have been reported successively. The conventional synthesis involves the condensation of dimedone with aromatic alde- hyde and malononitrile under refluxing in acetic acid [4] or the bicomponent condensation of dimedone with a-cyano- cinnamonitriles in the presence of ethanolic piperidine [5]. A number of methods have been reported for the synthesis of these compounds in the presence catalyst like 1,1,3, 3-N,N,N 0 ,N 0 -tetramethylguanidinium trifluoro acetate (TMGT) as an ionic liquid [6], diammonium hydrogen phosphate, (DAHP) [7], hexadecyldimethylbenzyl ammo- nium bromide [8] or by electrochemical reactions [9] or using microwave hating in the solid state [10] in organic solvents i.e. ethanol, methanol or in water [4–8]. However, most of rely on multi step reactions and each of the above methods has its own merits. However, these procedures have drawbacks, which involve reacting at high temperature, using of expensive catalyst, the low yield or commercially unavailable. 2 Experimental Malononitrile, aldehydes and a-hydroxy or a-amino acti- vated C–H acids were commercially available, obtained from Merck Chemical Co. and used without further puri- fication. Melting points were obtained with a Gallenkamp melting point apparatus. IR spectra were recorded on a Mattson 1000 FT-IR spectrometer. 2.1 Catalyst Preparation The catalysts used in this study were obtained by rehydrated Mg(OH) 2 at 450 °C for 2 h. A calcination temperature of 400–500 °C gave maximum conversion. When the catalyst was calcined above 500 °C, the activity of MgO decreased and continued to decrease as the calcination temperature increased. The maximum surface area was obtained after calcining the samples at 400–500 °C[11, 12]. M. Seifi Á H. Sheibani (&) Department of Chemistry, Shahid Bahonar University of Kerman, Kerman 76169, Iran e-mail: hsheibani@mail.uk.ac.ir 123 Catal Lett (2008) 126:275–279 DOI 10.1007/s10562-008-9603-5