12-Tungstoboric acid (H 5 BW 12 O 40 ) as an efficient Lewis acid catalyst for the synthesis of chromenopyrimidine-2,5-diones and thioxochromenopyrimidin-5-ones: Joint experimental and computational study Majid M. Heravi a, * , Tayebeh Hosseinnejad a , Mehrnoush Tamimi a , Vahideh Zadsirjan a , Masoud Mirzaei b, ** a Department of Chemistry, Alzahra University, POBox 1993891176, Vanak, Tehran, Iran b Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, 91775-1436, Mashhad, Iran article info Article history: Received 9 September 2019 Received in revised form 14 December 2019 Accepted 16 December 2019 Available online 19 December 2019 Keywords: H 5 BW 12 O 40 Lewis acid Heteropoly acids Chromenopyrimidine-2,5-diones Thioxochromenopyrimidin-5-ones Multicomponent reaction Density functional theory abstract H 5 BW 12 O 40 (BWA), Keggin-type heteropoly acid was employed as an effective, eco-friendly and reusable Lewis acid catalyst for the high yielding synthesis of chromenopyrimidine-2,5-diones and thio- xochromenopyrimidin-5-ones via multicomponent reaction (MCR) of differently substituted benzalde- hydes, urea/thiourea, and 4-hydroxycoumarin in refluxing water. The BWA catalyst could be recovered by a simple filtration and applied in three successive runs with no noticeable decrease in the yield. Inter- estingly, this catalyst structure pattern may act as useful model for the design and assembly of the functional molecule-based catalysts, especially in the field of molecular sieve materials. Moreover, thermochemical properties in the synthesis of title compounds were assessed using density functional theory (DFT) calculations. © 2019 Published by Elsevier B.V. 1. Introduction The development of safe materials with catalytic potencies is an attractive and important issue in material chemistry as well as sustainable chemistry. In general, catalysts accelerate and improve the chemical reactions, thus most organic transformations, should be performed under catalysis. Catalysis is the process of enhancing the rate of a chemical reaction by using a substance as a catalyst. A catalyst is not exhaust in the catalyzed reaction and can continue to act, continually [1 ,2]. Green chemistry, so-called sustainable chemistry, is a domain in chemistry and especially in the chemical industry, focused on the designing of reactions and industrial processes that minimize or remove the utilization and creation of hazardous materials [3]. Merits of green Chemistry are better human health cleaner air, less release of toxic chemicals to air, resulting less damage to lungs thus increased safety in the chemical industry; less use of toxic materials [4]. The catalytic behavior of heteropoly acids (HPAs) and poly- oxometalates (POMs) compounds are notable both in activity and reusability. POMs or HPAs, as a family of POMs, are a class of transition-metal oxide clusters like Mo, W, V, Nb and Ta which possess a large range of structures in terms of size, shape, elemental composition with high negative charge, along with varied redox properties, have attracted much attention of synthetic organic chemists as catalysts of choice. The most unique features of POMs which make them suitable acting as catalyst are their ease of controlling acidity, reduction potential, solubility, super acidity, excellent structural stability undergoing multi-electron redox cy- cles, low toxicity and corrosion. In the past decades, various HPAs and POMs have been employed as effective homogeneous and heterogeneous catalysts. * Corresponding author. ** Corresponding author. Department of Chemistry, Alzahra University, POBox 1993891176, Vanak, Tehran, Iran. E-mail addresses: mmh1331@yahoo.com, mmheravi@alzahra.ac.ir (M.M. Heravi), mirzaeesh@um.ac.ir (M. Mirzaei). Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: http://www.elsevier.com/locate/molstruc https://doi.org/10.1016/j.molstruc.2019.127598 0022-2860/© 2019 Published by Elsevier B.V. Journal of Molecular Structure 1205 (2020) 127598