%0 Journal Article
%T DABCO Catalyzed Synthesis of Xanthene Derivatives in Aqueous Media
%A Pradeep Paliwal
%A Srinivasa Rao Jetti
%A Anjna Bhatewara
%A Tanuja Kadre
%A Shubha Jain
%J ISRN Organic Chemistry
%D 2013
%R 10.1155/2013/526173
%X The reaction of 5,5-dimethylcyclohexane-1,3-dione with various heteroarylaldehydes afforded the corresponding heteroaryl substituted xanthene derivatives 1(a–f). The reaction proceeds via the initial Knoevenagel, subsequent Michael, and final heterocyclization reactions using 1,4-diazabicyclo[2.2.2]octane (DABCO) as a catalyst in aqueous media. The synthesized heteroaryl substituted xanthenes 1(a–f) reacted with malononitrile to obtain different alkylidenes 2(a–f). Short reaction time, environmentally friendly procedure, avoiding of cumbersome apparatus, and excellent yields are the main advantages of this procedure which makes it more economic than the other conventional methods. 1. Introduction In the past few decades, the synthesis of new heterocyclic compounds has been a subject of great interest due to their wide applicability. The importance of multicomponent reactions in organic synthesis has been recognized, and considerable efforts have been focused on the design and development of one-pot procedures for the generation of libraries of heterocyclic compounds [1, 2]. Multicomponent reactions (MCRs) have emerged as an important tool for building of diverse and complex organic molecules through carbon-carbon and carbon-heteroatom bond formations taking place in tandem manner [3]. Particularly, in the last three decades a number of three- and four-component reactions have been developed [4–6]. Xanthene derivatives are very important heterocyclic compounds and have been widely used as dyes [7] and fluorescent materials for visualization of biomolecules and in laser technologies [8]. They have also been reported for their agricultural bactericide activity [9] and anti-inflammatory [10] and antiviral activity [11]. These compounds are also utilized as antagonists for paralyzing action of zoxazolamine and in photodynamic therapy [12]. Due to their wide range of applications, these compounds have received a great deal of attention in connection with their synthesis. A wide variety of methods for the preparation of the xanthenes have been reported [13–19]. However, many of these methods are associated with several shortcomings such as long reaction times (16？h to 5 days), expensive reagents, harsh conditions, low product yields, and use of toxic organic solvents. Diazabicyclo[2.2.2]octane (DABCO) is an inexpensive, nontoxic, and commercially available catalyst that can be used in laboratory without special precautions [20–22]. But, it has not been used as a catalyst in xanthene synthesis; only a few reports are therein the literature [23–25]. This
%U http://www.hindawi.com/journals/isrn.organic.chemistry/2013/526173/