J. Indian Chern. Soc., Vol. 90, October 2013, pp. 1681-1694 Eco-friendly synthesis of condensed nitrogen heterocycles A brief experience from our groupt Manas Chakrabarty 0 * and Ajanta Mukherjib °Formerly, Department of Chemistry, Bose Institute, 9311, Acharya Prafulla Chandra Road, Kolkata-700 009, India E-mail : chakmanas09@gmail.com bDepartment of Chemistry, Krishnagar Government College, Krishnagar-741 I 01, Nadia, West Bengal, India Manuscript received 05 July 2013. accepted 06 July 2013 Abstract : In order to develop ceo-friendly syntheses of condensed nitrogen heterocycles, solvent-free syntheses on solid acidic catalysts and aqueous reactions using a phase transfer catalyst (PTC) were successfully carried out. The cata- lysts used were (i) TLC-grade silica gel G (Si0 2 ), (ii) Si0 2 doped with 10 mol% phosphoric acid (H 3 P0 4 -Si0 2 ), (iii) Montmorillonite K10 clay (K10), (iv) acid-washed K10 clay (acid-clay), (v) KIO doped with one equivalent (with respect to substrate) of tosic acid (TsOH-KIO) and (vi) cetylpyridinium bromide (CPB) (5 mol%) as the PTC. The reactions were carried out at room temperature (rt), at 60-70 •c (oven) or under microwave irradiation (MWI). Keywords : Heterocycles, ceo-friendly synthesis, solvent-free, aqueous, green catalysts. Introduction During the last decade, we worked on the synthesis and reactions of condensed nitrogen heterocycles since heterocyclic compounds play a major and significant role in our everyday life 1 a. In the early twentieth century, a chemist with foresight, G. Ciamician observed that the then extant syntheses of compounds related to natural products required harsh conditions and excess energy. He commented that actual advancement in synthetic chem- istry would mean to be able to synthesise compounds in a mild way as nature does. He meant development of envi- ronment-friendly chemistrylb-c. Oecades later, the grow- ing conflict between the ever increasing pollution of en- vironment by the industries on one hand and the undeni- able need to develop industries, specially chemical indus- tries, on the other hand led IUPAC to float the philoso- phy of "Sustainable Chemistry" whose objective was to develop ways and means of pursuing chemistry in an environment-friendly manner 2 . Paul Anastas, a Member of a related IUPAC Committee, coined the term "Green Chemistry" which was defined as the "invention, design and application of chemical products and processes to reduce or to eliminate the use and generation of hazard- ous substances 3 . In our work, we resorted to the following out of the twelve principles of Green Chemistry 4 : (i) the use of harmless acidic, basic and neutral solids with large sur- face areas as catalysts, (ii) the carrying out of reactions in a solvent-free manner and in water and (iii) the use of an alternative non-conventional source of energy, viz. mi- crowave (MW). The catalysts that we employed are Montmorillonite KlO clay (KlO), named after Montmorillon of France and perhaps the most widely explored catalyst in solvent- free reactions 5 , silica gel G (TLC-grade; Si0 2 ), neutral alumina and a phase transfer catalyst (PTC; in reactions in water). Whenever a more acidic catalyst was necessi- tated, we used acid-washed KlO clay (designated "acid- clay"), KlO clay doped with rosie acid (TsOH-KIO) and silica gel G doped with phosphoric acid (H 3 P0 4 -Si0 2 ). The required concentrations of tosic acid and phosphoric acid were determined by trial experiments. In our so called solvent-free reactions, the reactants were dissolved in required minimum of solvents, adsorbed tin honour of Professor Sunil Kumar Talapatra on the occasion of his 80th birthday. 1681