**1. Introduction**

Green chemistry, also known as sustainable chemistry, is an area of chemistry and chemical engineering which focus on the design of products and processes that minimize or eliminate the use and generation of hazardous substances [1]. In 1998, Paul Anastas and John C. Warner reported a set of 12 green chemistry principles [2]. Use of green chemistry can help us to create alternatives to hazardous sub stances. Chemical processes can be designed which reduce waste and prevent diminishing of natural resources. Processes can be designed that use lesser amounts of energy. Heterocyclic compounds had a special place among pharmaceutically important natural products and synthetic molecules. Among the heterocycles, nitrogen based molecules are abundant in nature and is of utmost importance to life because their structural subunits exists in natural products like hormones, vitamins, antibiotics, alkaloids,

herbicides, Nucleic acid (DNA and RNA) etc [3]. The construction of complicated cyclic target molecules having minimum environment impact is a challenging task for academicians, scientists and industry people. Greener methods are required for the synthesis of N-heterocycles as these compounds are medicinally important [4, 5]. Environment friendly protocols have been explored all over the globe for heterocyclic synthesis to improve energy consumption, atom economy and reaction yields [6, 7]. In the past few decades, numerous research papers have reported the use of water as green solvent [8, 9]. Researchers are also making use of polyethylene glycol for its low price and low acute toxicity [10, 11]. More recently, research teams have demonstrated that the use of bio-based solvents is also a solvent of choice [12]. All these results prove that the concepts of green chemistry have made remarkable progress. The conventional methods for the synthesis of N-heterocyclic skeleton require the use of expensive starting materials and high temperature. Chemists play an important role in the construction of a sustainable future through the application of greener chemical processes. As so, the development of new synthetic methods using more efficient energy sources and less hazardous solvents as well as renewable and eco-friendly catalysts to attain the N-heterocyclic core can provide significant environmental and economic advantages.
