February 2013 DBU Promoted Facile Synthesis of New Thieno[2,3‐b]pyridine/ quinoline Derivatives and Their Antimicrobial Evaluation E131 Chebolu Naga Sesha Sai Pavan Kumar, a Ejjirothu Srihari, a Mettu Ravinder, a Koochana Pranay Kumar, b U. S. N. Murthy, b * and Vaidya Jayathirtha Rao a * a Organic Chemistry Division II, Indian Institute of Chemical Technology, Uppal Road, TarnakaHyderabad‐500 607, India b Biology Division, Indian Institute of Chemical Technology, Uppal Road, TarnakaHyderabad‐500 607, India * E-mail: jrao@iict.res.in; usnmurthy@iict.res.in Received April 21, 2011 DOI 10.1002/jhet.1091 Published online 7 March 2013 in Wiley Online Library (wileyonlinelibrary.com). Several new thieno[2,3‐b]pyridine and thieno[2,3‐b]quinoline derivatives are synthesized in an efficient manner catalyzed by DBU as a base. Simple workup procedure, good yields, and mild reaction conditions are the salient features of this method. All the synthesized compounds are screened for antimicrobial activity against several organisms. J. Heterocyclic Chem., 50, E131 (2013). INTRODUCTION In organic chemistry, derivatives of pyridine and its fused analogs are the important class of heterocyclic compounds, and they attract considerable interest because of their great practical usefulness, primarily, due to their various biological activities [1]. In addition, many pyridines are reported to be useful as herbicides, bactericides, fungi- cides, insecticides, and pharmaceuticals [2]. In particular, several thienopyridine/thienoquinoline derivatives are known to possess antibacterial [3], antifungal [4], antiviral [5], anti‐inflammatory [6], antihypertensive [7], antiparasitic [8], and gonadotropin releasing hormone‐antagonizing activ- ities [9]. Due to their isosterism with indolopyridines or isoquinolines, thienopyridines have attracted much attention because of their potential biological activity as antipsycho- tics [10], antibacterians [11], LH‐receptor agonists [12], and Src kinase inhibitors [13]. In addition, certain thienoder- ivatives hold promise for the treatment of osteoporosis and serve as tachykinin antagonists, 5‐lipoxygenase inhibitors with a broad spectrum of action, acetylcholinesterase inhibi- tors [14]. Thieno[2,3‐b]pyridines have been claimed as anti- cancer agents with inhibitory action against the VEGF‐2 receptor tyrosine kinase [15]. The antitumor activity of 6‐ aryl‐3‐amino‐thieno[2,3‐b]pyridine derivatives is also reported by Zeng and coworkers [16]. Recently, thieno[2,3‐ b]pyridines reported as potassium channel inhibitors [17]. Thieno[2,3‐b]pyridine derivatives have been previously pre- pared in a multistep procedure from either a thiophene or a pyridine ring and further ring closure leading to the other heterocyclic fused system. Unfortunately, many of these methods suffer from limitations such as long reaction times, low to moderate yields, and co‐occurrence of several side products. Very few reports are available for the direct synthe- sis of thieno derivatives from corresponding 2‐chloro 3‐car- baldehydes. Suárez et al. [18] reported the preparation of 4,7‐dihydrothieno[2,3‐b]pyridines from the o‐chloroformyl substituted 1,4‐dihydropyridines using sodium ethoxide and dry ethanol under inert atmosphere. Bhat et al. [19] reported the one‐step synthesis of 2‐methoxycarbonylthieno[2,3‐b]qui- nolines from 2‐chloroquinoline‐3‐carbaldehydes using potas- sium carbonate in tetrahydrofuran with good yields. The efficiency of DBU (1,8‐diazabicyclo[5.4.0]undec‐7‐ ene) as a non‐nucleophilic, sterically hindered, tertiary amine base in organic chemistry has been widely demonstrated [20]. In particular, it has been widely used for carrying out dehydrohalogenation reactions. In many instances, DBU itself reacted with different α,β‐unsaturated systems, resulting in the formation of ε‐caprolactam derivative. The reagent is com- mercially available and has been extensively used for carrying out a wide range of reactions [21]. Motivated by these find- ings, and in continuation of our ongoing efforts endowed with the discovery of nitrogenated heterocycles [22], herein we re- port the facile synthesis and antimicrobial activity of various thienopyridines and thienoquinolines using DBU as mild base. In the present study, we have used various 2‐chloro nico- tinaldehydes (1a–e, i, j) as active substrates which were devel- oped in our laboratory [23]. The condensation reaction proceeded smoothly under mild conditions, upon treatment of methyl thioglycolate and DBU in THF with aldehyde. © 2013 HeteroCorporation