%0 Journal Article
%T Microwave-Assisted Synthesis of Spirofused Heterocycles Using Decatungstodivanadogermanic Heteropoly Acid as a Novel and Reusable Heterogeneous Catalyst under Solvent-Free Conditions
%A Srinivasa Rao Jetti
%A Divya Verma
%A Shubha Jain
%J Journal of Catalysts
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/392162
%X Decatungstodivanadogermanic acid (H6GeW10V2O40¡¤22H2O) was synthesized and used as a novel, green heterogeneous catalyst for the synthesis of spirofused heterocycles from one-pot three-component cyclocondensation reaction of a cyclic ketone, aldehyde, and urea in high yields under solvent-free condition in microwave irradiation at 80¡ãC. This catalyst is efficient not only for cyclic ketones, but also for cyclic ¦Â-diketones, ¦Â-diester, and ¦Â-diamide derivatives such as cyclohexanone, dimedone, and Meldrum's acid, or barbituric acid derivatives. 1. Introduction Dihydropyrimidinones and their derivatives have attracted great attention recently in synthetic organic chemistry due to their pharmacological and therapeutic properties such as antibacterial and antihypertensive activity as well as behaving as calcium channel blockers, ¦Á-1a-antagonists [1], and neuropeptide Y (NPY) antagonists [2]. The biological activity of some alkaloids isolated recently has been attributed to a dihydropyrimidinone moiety [3]. The first procedure to these compounds reported by Biginelli [4] more than a century ago makes use of the three-component, one-pot condensation of a ¦Â-ketoester, an aldehyde, and a urea under strongly acidic conditions [4]. However this method suffers from low yields in the case of substituted aromatic and aliphatic aldehydes [5]. Owing to the versatile biological activity of dihydropyrimidinones, development of an alternative synthetic methodology is of paramount importance. Recently, many reviews [8, 9] and papers for preparing these compounds have been reported including classical conditions, with microwave and ultrasound irradiation and by using some other different catalysts such as phosphorus pentoxide-methanesulfonic acid [10], potassium terbutoxide (t-BuOK) [11], ammonium dihydrogen phosphate [12], silica-gel [13], mesoporous molecular sieve MCM-41 [14], cyanuric chloride [15], nano-BF3¡¤SiO2 [16], silica gel-supported polyphosphoric Acid [17], zirconium(IV) chloride [18], indium(III) bromide [19], ytterbium(III)-resin [20], 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMImBF4) or hexafluorophosphorate (BMImPF6) [21], ceric ammonium nitrate (CAN) [22], Mn(OAc)3¡¤2H2O [23], lanthanide triflate [24], indium(III) chloride [25], lanthanum chloride [26], H2SO4 [27], montmorillonite KSF [28], polyphosphate ester (PPE) [29], BF3-OEt2/CuCl/HOAc [30], and conc. HCl [31, 32]. However, in spite of their potential utility, many of these methods involve expensive reagents, strongly acidic conditions, long reaction times, high temperatures, and stoichiometric
%U http://www.hindawi.com/journals/jcat/2013/392162/