This journal is c The Royal Society of Chemistry 2012 Catal. Sci. Technol., 2012, 2, 201–214 201 Cite this: Catal. Sci. Technol., 2012, 2, 201–214 Silica nanoparticles efficiently catalyzed synthesis of quinolines and quinoxalinesw Alireza Hasaninejad,* a Mohsen Shekouhy a and Abdolkarim Zare* b Received 20th August 2011, Accepted 17th September 2011 DOI: 10.1039/c1cy00332a In this work, highly efficient, green and inexpensive procedures for the preparation of quinoxaline and quinoline derivatives as attractive aza-polycyclic compounds are described. Silica nanoparticles-catalyzed condensation of 1,2-diamines with 1,2-diketones under solvent-free conditions at room temperature affords high yields of quinoxalines with short reaction times. Moreover, the microwave-assisted Friedla¨nder hetero-annulation reaction between 2-aminoaryl ketones and carbonyl compounds in the presence of silica nanoparticles (NPs) as catalysts gives high yields of quinoline derivatives with short reaction times. These reactions have been done in neutral conditions. The NPs catalysts can be reused without lost of activity even after recycling fourteen times . 1. Introduction Currently, the green synthesis of products without using volatile and toxic organic solvents is the subject of considerable interest in organic synthesis. 1 In this regard, solvent-free conditions have received tremendous attention. 1–4 Solvent-free conditions often lead to shorter reaction times, increased yields, easier workup, matching with the green chemistry protocols, and may enhance the regio- and stereoselectivity of reactions. Scale-up is also facilitated by the use of solvent-free techniques. 1–4 SiO 2 is a very inexpensive, recyclable, and commercially available oxide which has been extensively used as a support, accompanied with a catalyst, in organic transformations. 5–9 Nevertheless, the application of silica gel, solely, as a catalyst and a surface has been reported in few cases. 10–14 Recent research has shown that remarkable improvement in the catalytic activity of catalysts can be achieved by manipulating their composition and/or structure at a level of a few nanometres. 15–17 The development of new catalysts by nanoscale design has emerged as a fertile field for research and innovation. 15–17 The ability of nanotechnology to enhance catalytic activity opens the potential to replace expensive catalysts with lower amounts of inexpensive nanocatalysts. 15–17 Quinoxalines and quinolines are two important groups of aza-polycyclic compounds which have many biological and pharmaceutical properties. For example, quinoxalines have been applied as antimycobacterial, 18 antibacterial, 19 antifungal, 19 anthelmintic, 20 antidepressant 21 and antitumor agents. 22 Quinolines have been used as antimalarial, antiasthmatic, antihypertensive, antibacterial and tyrosine kinase inhibiting agents. 23,24 The condensation of 1,2-diamines with 1,2-diketones has been used as a useful synthetic route toward quinoxalines. For this transformation some catalysts such as, Yb(OTf) 3, 25 Zr(DS) 4, 26 (NH 4 ) 6 Mo 7 O 24 Á4H 2 O, 27 oxalic acid, 28 Zn[(L)proline], 29 iodine in DMSO, 30 and sulfamic acid/MeOH 31 have been reported. The Friedla¨nder hetero-annulation reaction has been used as a straightforward method for the synthesis of quinoline derivatives. 32,33 In this protocol, quinolines have been prepared by acid or base catalyzed condensation of 2-aminoaryl ketones with carbonyl compounds possessing a reactive a-methylene group followed by cyclodehydration. 32–38 However, many of the reported protocols for the synthesis of quinoxalines and quinolines suffer from disadvantages such as, the use of expensive catalysts, the necessity for anhydrous conditions, prolonged reaction times, unsatisfactory yields, difficult experi- mental as well as workup procedures and the use of volatile organic solvents. Moreover, some methods need multi-steps procedures. Consequently, the development of efficient, inexpensive and simple methods for the preparation of quinoxaline and quinoline derivatives under solvent-free conditions is in demand. Considering the above subjects and in continuation of our interest on the synthesis of aza heterocyclic compounds, 39 herein we report highly efficient and simple methods for the synthesis of quinoxalines from 1,2-diamines and 1,2-diketone at room tempera- ture as well as the synthesis of quinolines from 2- aminoaryl ketones and carbonyl compounds under microwave irradiation in the presence of silica nanoparticles (NPs) as catalysts under solvent- free conditions (Scheme 1). It is worth noting that our presented work has none of the above-mentioned disadvantages at all. a Department of Chemistry, Faculty of Sciences, Persian Gulf University, Bushehr 75169, Iran. E-mail: ahassaninejad@yahoo.com; Fax: +98(771)4541494; Tel: +98(771)4222319 b Chemistry Department, Payame Noor University, 19395-4697 Tehran, I. R. of Iran. E-mail: abdolkarimzare@yahoo.com; Fax: +98(771)5559489; Tel: +98(771)559486 w Electronic supplementary information (ESI) available: See DOI: 10.1039/c1cy00332a Catalysis Science & Technology Dynamic Article Links www.rsc.org/catalysis PAPER Downloaded on 10 December 2011 Published on 27 October 2011 on http://pubs.rsc.org | doi:10.1039/C1CY00332A View Online / Journal Homepage / Table of Contents for this issue