Synthesis of Pyranoquinolines from One-Pot Imino-Diels-Alder Reaction catalyzed by LaCl3.7H2O

Abstract

The Hetero-Diels-Alder reaction is one of the most powerful synthetic routes for constructing nitrogen containing sixmembered heterocycles [1]. In recent years, increasing attention has been given to the synthesis of pyrano[3,2-c] tetrahydroquinolines via three component aza-Diels–Alder reactions of aryl aldehyde, aryl amine with cyclic enol ethers. pyrano quinolone derivatives are an important class of natural products and exhibit spectrum of biological activities, such as antiallergic, anti-inflammatory, antipyretic, analgesic, antiplatelet, psychotropic, estrogenic activity anti-arrhythmic, immunosuppressive and anticancer properties [2]. In addition to this they are also used in pharmaceuticals [3].<br><br>In this report, we describe a novel and highly efficient method for the one-pot synthesis of pyranoquinolines using a catalytic amount of LaCl3 .7H2O. Thus treatment of aniline with 3,4-dihydro-2H-pyran (DHP) in the presence of 5 mol% lanthanum trichloride in acetonitrile under reflux afforded the corresponding pyrano[3,2-c]quinolone derivatives endo and exo in 90% yield (Scheme 1).<br><br>RNH2NHONHOOHOHHHHHRRCH3CNLaCl3.7H2Orefluxendo(major)exo(minor)O<br><br>(Scheme1)<br><br>References<br><br>[1]. Yadav, J. S.; Reddy, B. V. S.; Srinivasa Rao, R.; Kiran Kumar, S.; Kunwarb, A. C. InClR3R<br><br>Catalyzed hetero-Diels–Alder reaction: an expeditious synthesis of pyranoquinolines. Tetrahedron.<br><br>2002, 58, 7891-7896.<br><br>[2]. Palaniappan, S.; Rajender,B.; Umashankar, M. Controllable stereoselective synthesis of cis or trans pyrano and furano tetrahydroquinolines: Polyaniline-p-toluenesulfonate salt catalyzed one-pot aza-Diels–Alder reactions. J. Mol. Catal. A-Chem. 2012, 352, 70-74.<br><br>0B[3]. Michael, J.P. Quinoline, quinazoline and acridone alkaloids. Nat. Prod. Rep. 2005, 22, 627-646