Oxalic acid as a catalyst for efficient synthesis of bis-(indolyl)methanes, and 14-aryl-14H-dibenzo[a,j]xanthenes in water Nagnnath D. Kokare a,b , Jaiprakash N. Sangshetti a , Devanand B. Shinde a, * a Department of Chemical Technology, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad 431004 (MS), India b New Drug Discovery, Wockhardt Research Centre, Aurangabad 431210 (MS), India Received 7 April 2008 Abstract A simple, efficient, and environment benign route was developed for the preparation of bis-(indolyl)methanes and 14-aryl-14H- dibenzo[a,j]xanthenes from condensation of various aromatic aldehydes or ketones with indole, and 2-naphthol, respectively, using oxalic acid catalyst in aqueous medium. Use of cheap and easily available catalyst, better yields and simple reaction protocol are the advantages of the present method. # 2008 Devanand B. Shinde. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Oxalic acid; Bis-(indolyl)methanes; 14-Aryl-14H-dibenzo[a,j]xanthenes; Aldehydes In recent years, synthetic chemists had taken tremendous interest to develop highly efficient transformations for the synthesis of bis-compounds of indoles, and 2-naphthols to give corresponding bis-(indolyl)methanes, and 14-aryl- 14H-dibenzo[a,j]xanthenes due to their potential applications in the pharmaceutical and agrochemical industries, and synthetic chemistry. Indole and bis-(indolyl)alkane moieties are present in number of naturally occurring compounds [1]. These compounds have the vast applications in material sciences, agrochemicals, and pharmaceuticals [2]. Particularly, the substrates including bis-(indolyl)methane moieties such as secondary metabolites [3], and marine sponge alkaloids [4], are of remarkable significant. Literature reveals number of synthetic methods for preparation of bis-(indolyl)alkane derivatives from condensation of the indole with various aldehydes and ketones in the presence of catalysts like Lewis acids, protic acid, rare earth catalysts such as La(OTf) 3 , In(OTf) 3 , InCl 3 , and ionic liquids [5]. Xanthenes, and their derivatives like benzoxanthenes, have wide range of biological and therapeutic properties such as antibacterial, antiviral and anti-inflammatory activities [6]. Recently, these compounds were used in photodynamic therapy and for antagonism of the paralyzing action of zoxazolamine [7]. These compounds were also widely used as dyes [8], in laser technologies [9], and in fluorescent materials for visualization of biomolecules [10]. Literature reveals number of synthetic methods for preparation of xanthenes and benzoxanthenes including cyclodehydrations [11], trapping of benzynes by phenols [12], cyclocondensation between 2-hydroxyaromatic aldehydes and 2-tetralone www.elsevier.com/locate/cclet Available online at www.sciencedirect.com Chinese Chemical Letters 19 (2008) 1186–1189 * Corresponding author. E-mail address: dbschemtech@hotmail.com (D.B. Shinde). 1001-8417/$ – see front matter # 2008 Devanand B. Shinde. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.07.015