RESEARCH ARTICLES CURRENT SCIENCE, VOL. 116, NO. 6, 25 MARCH 2019 936 *For correspondence. (e-mail: vbhelavi@gmail.com) Green protocol for the synthesis of 1,8-dioxo-decahydroacridines by Hantzsch condensation using citric acid as organocatalyst Monika Patil 1 , Shrikrishna Karhale 1 , Ananada Kudale 1 , Arjun Kumbhar 2 , Sagar More 2 and Vasant Helavi 1, * 1 Department of Chemistry, Rajaram College, Kolhapur 416 004, India 2 Department of Chemistry, P. D. V. P. College, Tasgaon 416 312, India Herein we describe a clean and sustainable, one-pot, multi-component protocol for the synthesis of 1,8- dioxo-decahydroacridines by Hantzsch condensation of cyclic 1,3-dicarbonyl compound and NH 4 OAc with diverse aryl aldehydes using citric acid as an inexpen- sive green additive in ecological safe solvent. Utiliza- tion of cheaper and safer catalyst, cleaner reaction profile, straightforward work-up procedure and good to excellent yields of the desired product are the note- worthy aspects of this method. Keywords: Acridines, citric acid, organocatalysts, green protocol, multi-component reactions. OUR environment needs to be protected from the growing amounts of waste and toxic by-products that sequentially lead to chemical pollution. Therefore, synthetic chemists are interested to develop relatively safer technologies which play a vital role in green chemistry. Establishing newer chemical transformations should satisfy the green principles such as non-toxic, non-flammability, eco- friendly medium, and separation as well as recycling of the catalysts. Since the last decade, efforts have been made towards the design and synthesis of an environ- ment-friendly method with respect to reagents, catalysts and solvents that could be easily biodegradable 1,2 . Multi- component reaction (MCR) strategies have been widely used in the convergent synthesis of complex organic enti- ties. The MCRs uses simple and easily available starting materials and provide high atom economy and selectivity. It is one of the important synthetic tools available to achieve both economic and environment-friendly goals. Therefore, the synthesis of heterocyclic compounds using significant bioactivities with MCR support is an impor- tant pursuit in organic synthesis. Synthesis of acridines is a growing area of interest due to polyfunctionalized groups with a wide range of biolo- gical activities 3 . Among them, 1,8-dioxo-decahydro- acridines is an important class of aza-heterocycles in which a phenyl-substituted pyridine ring is fused with two cyclohexanone rings. These structures contain 1,4- dihydropyridine (1,4-DHP) as a parent core, which acts as fluorescent probes in bioanalytical chemistry 4 and also used as potential drug candidates for the treatment of car- diovascular diseases. Some of these compounds are used in dye-sensitized solar cells and in the preparation of blue light-emitting devices 5,6 . In addition, 1,8-dioxo- decahydroacridines have been widely employed as DNA intercalators, SIRT1 inhibitors, and calcium and potas- sium channel modulators 7,8 . Several studies have revealed that these heterocycles exhibit numerous medicinal applications which include antitumour, calcium-channel blockers, antileukemic, antifungal, anticancer, anti-athero- sclerotic and bronchodilator 9–13 . They are also used as laser dyes, chemosensors and initiators in the photo- polymerization process. These derivatives are highly important due to their structural similarities with coen- zyme nicotinamide adenine dinucleotide (NADH), which plays an important role in biological systems. The most common route for the synthesis of 1,8-dioxo- decahydroacridines is the condensation of a diverse range of aryl aldehydes, dimedone or cyclic 1,3-dicarbonyl compounds with various nitrogen sources such as ammo- nium acetate, urea, ammonium hydroxide, ammonium bicarbonate and hydroxylamine 14–18 . A variety of catalysts such as sulphonated polyethylene glycol (PEG–OSO 3 H), silzic (SiO 2 –ZnCl 2 ), silica boron–sulphuric acid, proline, Zn(OAc) 2 , nano nickel cobalt ferrite (Ni 0.5 Co 0.5 Fe 2 O 4 ), carbon-based solid acid, Bronsted acidic imidazolium salts, ascorbic acid, acetic acid, tris(pentafluorophenyl) borane/B(C 6 F 5 ) 3 , silica-supported polyphosphoric acid, ammonium chloride, silica-supported Preyssler nanopar- ticles have been employed in this reaction 19–32 . However, most of these reported methods have certain drawbacks such as use of toxic and corrosive solvents, expensive reagents, tedious preparation of catalyst, prolonged reac- tion times, complicated work-up procedure, harsh reaction