FULL PAPER Ag 3 [PMo 12 O 40 ]: An efficient and green catalyst for the synthesis of highly functionalized pyran‐annulated heterocycles via multicomponent reaction Mehrnoush Tamimi 1 | Majid M. Heravi 1 | Masoud Mirzaei 2 | Vahideh Zadsirjan 1 | Nahid Lotfian 1 | Hossein Eshtiagh‐Hosseini 2 1 Department of Chemistry, School of Science, Alzahra University, PO Box 1993891176, Vanak, Tehran, Iran 2 Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, 917751436 Mashhad, Iran Correspondence Majid M. Heravi, Department of Chemistry, School of Science, Alzahra University, PO Box 1993891176, Vanak, Tehran, Iran. Email: mmh1331@yahoo.com; mmheravi@alzahra.ac.ir A facile, efficient and eco‐friendly catalytic protocol was developed for the syn- thesis of medicinally important pyran‐annulated heterocycles via multicompo- nent reaction (MCR). Cyclocondensation of differently substituted aromatic aldehydes, malononitrile/ethyl cyanoacetate and various β‐dicarbonyl com- pounds in the presence of Ag 3 [PMo 12 O 40 ]⋅nH 2 O as heterogeneous catalyst, in EtOH–H 2 O, afforded diverse pyran‐fused chromene analogues. The merits observed for this approach were it being conducted via MCR, using commer- cially available or easily accessible starting materials in the presence of a green and easily separable heterogeneous and reusable catalyst, and affording high yields of desired products in very short reaction times with high purity in one‐pot fashion, thus providing a superior alternative approach for the synthe- sis of pyran‐annulated heterocycles. KEYWORDS 2‐amino‐4H‐pyrans, Ag 3 [PMo 12 O 40 ], heterogeneous catalysis, multicomponent reaction, one‐pot synthesis, polyoxometalates 1 | INTRODUCTION Nowadays, the design, preparation and use of efficient and environmentally friendly catalysts are important chal- lenges in synthetic organic chemistry. Polyoxometalates (POMs), as anionic metal–oxygen nanoclusters, are considered as important inorganic catalysts for such purposes. [1] Due to the multiple active sites, including protons, metal atoms and oxygen atoms, POMs have been used extensively as versatile catalysts in organic synthesis. In POMs, protons give Brønsted acid characters, thus pro- moting acid‐catalysed reactions. Accepting this general idea, for choosing them as catalysts, attention should be focused on the metal ions of POM structures. Those metal ions that possess unoccupied orbitals are favourable since they can accept electrons thus gaining Lewis acid characters and as result the selected POMs possess higher acidic character which is beneficial for acid‐catalysed reactions. [2] POM‐acid‐catalysed reactions have been well established over the years. Among them, Keggin‐type POMs with the general formula H n [XM 12 O 40 ] (X is the central heteroatom and M is the addenda atom) have attracted much attention. [3] They possess stable structures and strong acidity, which can be tuned by simply chang- ing the polyanion chemical composition and the cationic moiety. Unhelpfully, pure bulk POMs have relatively small specific surface areas that hinder accessibility to active sites, thus affecting their catalytic activity. More- over, their high solubility in many polar solvents favours them in the homogeneous phase. Although these homo- geneous catalysts are remarkably efficient, their separa- tion and recovery are difficult and as a result their reusability is uncertain. Received: 5 February 2019 Revised: 21 April 2019 Accepted: 13 May 2019 DOI: 10.1002/aoc.5043 Appl Organometal Chem. 2019;33:e5043. https://doi.org/10.1002/aoc.5043 © 2019 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/aoc 1 of 11