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In continuation of our previous works on the application of (NH 4 ) 42 72 ], a Keplerate-type giant-ball nanoporous isopolyoxomolybdate, as a catalyst for the synthesis of heterocyclic compounds, in this paper, we report another application of this attractive catalyst in the synthesis of 2-amino-5-oxo-4,5-dihydropyrano[3,2-c]chromene-3-carbonitriles via a onepot three-component reaction of 4-hydroxycoumarin, aldehydes and malononitrile. The reactions occur in ethanol-water as solvent at room temperature and the process is operative with various aldehydes, giving the corresponding products in high yields. Other beneficial features of this protocol include short reaction times, simple work-up and the recyclability and reusability of the catalyst for up to five consecutive runs. Copyright © 2016 John Wiley & Sons, Ltd.Additional supporting information may be found in the online version of this article at the publisher's web site.Keywords: dihydropyrano[3,2-c]chromenes; giant nanoporous isopolyoxomolybdate; Keplerate; {Mo 132 } IntroductionThe synthesis of dihydropyrano[3,2-c]chromenes with biological and pharmacological properties such as spasmolytic, diuretic, anticoagulant, anticancer and antianaphylactic activities [1,2] is currently of great interest. The reported protocol for the synthesis of dihydropyrano [3,2-c]chromenes involves the one-pot three-component reaction of 4-hydroxycoumarin, aldehydes and malononitrile in the presence of a catalyst such as polymer-supported sulfanilic acid, [3] saccharose, [4] [9] NaCl, [10] crown ether complex cation ionic liquid, [11] tetrabutylammonium bromide [12] and (NH 4 ) 2 HPO 4 or S-proline.[13]While each of these methods has its own advantages, many suffer from limitations such as prolonged reaction times, the use of relatively expensive catalysts and unsatisfactory yields. Thus the discovery of a new and efficient catalyst with high catalytic activity, short reaction times, recyclability and simple reaction work-up for the preparation of dihydropyrano[3,2-c]chromenes is of great interest. Heterogeneous catalysis has been known for many years and has become strategically vital for efficient and ecofriendly organic transformations over the past few decades. [14][15][16][17] These catalysts have many advantages over homogeneous catalysts involving simple work-up, ease of handling, recoverability and reusability. [18,19] Catalysts of this type have the potential to make the processes in which they are applied cleaner, safer, higher-yielding and relatively inexpensive. [20][21][22][23] Polyoxometalates (POMs) are a large class of metal oxide clusters of early transition metals, typically W(VI), V(V), Mo(VI), Nb(V) and Ta (V), bridged by oxygen atoms. They are of proven value in catalysis, magnetism, materials science and biomedicine, [24][25][26][27][28] because they are diverse and highly modifiable in size, shape, charge density, acidity and reversible redox potential. A number of very large POM anions have been synthesized and structurally characterized. Beginning w...

NH 4 ) 42 [Mo 72 VI Mo 60 V O 372 (CH 3 COO) 30 (H 2 O) 72 ], a Keplerate-type giant nanoporous isopolyoxomolybdate, denoted as ({Mo 132 }), was found to have extraordinary catalytic activity in the synthesis of 1,8-dioxo-octahydroxanthenes, and 1,8-dioxodecahydroacridines via one-pot reactions. The catalyst was prepared using inexpensive and readily available materials and characterized using FT-IR, and UV spectra. The desired products were obtained only within a few seconds in high yields under solvent-free conditions at 130°C. Furthermore, the procedures and work-ups were simple and the catalyst can be conveniently recovered and reused. To our knowledge, the catalyst exhibits the highest activity over other procedures available in the literature for the synthesis of the mentioned compounds.

Nano-Fe 3 O 4 encapsulated-silica particles bearing sulfonic acid groups (Fe 3 O 4 @SiO 2 -OSO 3 H) has been used as an efficient and magnetically separable heterogeneous catalyst for the synthesis of 1,2,4,5-tetrasubstituted imidazoles by one-pot, four-component reaction of benzil, aromatic aldehydes, primary amines, and ammonium acetate under neat conditions. The effect of various reaction parameters, such as reaction temperature, catalyst loading and solvent effect, were studied. The desired products are obtained in relatively short reaction times with high yields. Importantly, the catalyst could be easily separated from the reaction mixture by a permanent magnet and reused for several times without the significant loss of its activity.

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