**1. Introduction**

Among pharmaceutically relevant natural and synthetic compounds, heterocyclic compounds hold a unique place. They have an incredible ability to serve as biomimetics and potential pharmacophores and are standard key components of several drugs [1, 2]. There is a critical need for new small organic molecules both in lead identification and lead optimization processes. Conventional methods of organic synthesis are often too slow to satisfy the demand for generation of such compounds. The synthetic chemists worldwide have been under tremendous pressure to produce them in good numbers and that too in an environmentally benign fashion. A typical reaction involves a reaction medium apart from reactants and reagents to form products. There are several issues that influence the choice of solvent, especially in context of green chemistry. It should be relatively non-reactive, non-toxic and non-hazardous. The solvent should also be contained, that is, it should not be released into the environment [3].

Water is one of the most intriguing media among all the alternative solvents available, owing to its peculiar properties. It is the most abundant and available molecule on the planet and many biochemical processes occur in aqueous medium. Despite its accessibility, it has not been a favourite reaction medium for organic chemists because its presence causes the decomposition of organometallic reagents, which are used preferably in dry organic solvents. In fact, water has been generally

used to work-up organic reactions and, therefore, it has been associated with a waste-production step and to the consequent obvious problems of cleaning-up water from reactants' residues arises. The low solubility of most organic compounds in water (hampering their reactivity), and the instability of many intermediates and catalysts in water are perhaps the two main causes of this problem. Today, it is a different scenario altogether. This very aqueous medium has captured the interest of organic chemists and many others, so much so that many surprising discoveries have been attributed to its use. Many organic reactions such as pericyclic, condensation, oxidation and reduction reactions can be conducted efficiently in aqueous medium and, in some cases, water is necessary to enhance the reaction rate and increase selectivity. Further, water-tolerant catalysts have been prepared that allow organometallic reactions to be carried out in aqueous medium. Reactions that were earlier thought impossible in water have today become a certainty [3].
