New Schiff base (SB) functionalized graphene oxide (GO) nanosheets containing phosphomolybdic counter‐anion H2PMo12O40¯ (H2PMo) were successfully prepared by grafting of 3‐aminopropyltriethoxysilane (APTS) on GO nanosheets followed by condensation with benzil and finally reaction with phosphomolybdic acid (H3PMo12O40, denoted as H3PMo) and characterized using Fourier transform infrared (FT‐IR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), particle size distribution, energy‐dispersive X‐ray (EDX) analysis, EDX elemental mapping, and inductively coupled plasma optical emission spectrometry (ICP‐OES). The prepared new nanomaterial, denoted as GO‐SB‐H2PMo, was shown to be an efficient heterogeneous catalyst in one‐pot, three‐component reaction of β‐naphthol, aldehydes, and dimedone, giving high yields of tetrahydrobenzo[a]xanthene‐11‐ones within short reaction times. The catalyst is readily recovered by simple filtration and can be recycled and reused several times with no significant loss of catalytic activity.

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...

The catalytic activity of newly prepared functionalized graphene oxide nanosheets, denoted as GO-SB-H2PMo, has been investigated in the synthesis of amidoalkyl naphthols through the one-pot, three-component reaction of β-naphthol with various aryl aldehydes and acetamide. The reactions occur under solvent-free conditions and the process is operative with various aryl aldehydes, giving the corresponding products in high yields over short reaction times. Moreover, the catalyst could be easily recovered from the reaction mixture and reused so that the considerable catalytic activity can still be achieved after the fifth run.