Chapter 19 - Microwave-Induced Synthesis of Heterocycles of Medicinal Interests

Abstract

Since 1986, a huge number of microwave-assisted organic/organometallic/inorganic transformations have been published with a growing number every year. It is well known that microwaves directly heat the reaction mixture without heating the glass wall of the reaction vessels. Thus, the “local heating” is avoided in microwave-induced chemical syntheses. Moreover, the dielectric constant (polarity) of the solvent(s) plays a pivotal role in microwave-assisted syntheses. Unnecessary formation of the by-products (wastes) is inhibited and the desired product is obtained in high yield. Because of these advantages, the use of microwaves to achieve chemical conversions is considered as green technology. On the other hand, heterocyclic compounds are widely distributed in nature and many of these possess medicinal/biological/pharmacological activity. In addition to nature-derived heterocycles, a large number of synthetic heterocycles are being used as medicines. The microwave-supported synthetic strategies for the synthesis of heterocycles are important objectives. This chapter describes the pertinent recent examples of microwave irradiation to accomplish various chemical transformations accelerated by a variety of catalysts, which include, but are not limited to, Lewis acids, other metal-containing catalysts, organocatalysts, heterogeneous catalysts, phase-transfer catalysts, solid-supported catalysts, inorganic catalysts (bases, acids, and salts), and so on. Interesting discussions on the synthesis of novel heterocycles, complexes, and pharmacophores are included. Since green and sustainable chemistry is an extremely emerging and comparatively new field of research, attempts to stimulate more activities on green medicinal chemistry are provided. Microwave-assisted synthesis of bioactive molecules in green solvents like aqueous media, ionic liquids, etc., is taken into account. Discussions related to the concurrent effect of microwaves, catalysts, and/or solvents; supports to constitute an expeditious and general route for the syntheses of a large number of medicinally important heterocyclic compounds, and pharmacophores are an important aspect of this chapter.