Microwave Assisted Synthesis of Five Membered Azaheterocyclic Systems

Abstract

Abstract: The present review provides a comprehensive summary of microwave-assisted preparation of five-membered azaheterocyclic systems, such as pyrrole, pyrazole, imidazole, triazole, thiazole, isothiazole, oxazole, isoxazole, oxadiazole, thiadiazole and tetrazole. Keywords: Azaheterocycles, Microwave, Synthesis. 1. INTRODUCTION Microwave energy has become a popular tool used in the syn-thesis of a variety of heterocyclic systems for a variety of reasons. Microwave energy offers tremendous advantages relative to tradi-tional heating, such as cleaner chemistry, reductions in reaction times, improved yields efficiency, product quality, and safety, as well as tremendous scope for automation. Synergy of this method-ology with reactions performed on support media, and/or in the absence of solvent, provides an environmentally clean technique that allows for the attainment of high yields of products at reduced energy costs. Heterocycles form the largest classical division of organic chemistry. They are of immense importance both in medicine and in industry, with many heterocyclic compounds being used as ac-tive intermediates. Among all heterocycles, five membered hetero-cyclic systems hold a prominent position as they constitute an inte-gral part of natural alkaloids, antibiotics, vitamins, nucleic acids, hormones and synthetic drugs. Microwave radiation was discovered as a method of heating in 1946 and has been used in chemistry since the 1970s. It was intro-duced to organic syntheses in the 1980's. Since then, terms such as MAOS (Microwave Assisted Organic Synthesis) and MORE (Mi-crowave induced Organic Reaction Enhancements) came in to us-age. Over the years, chemists have successfully conducted a large range of organic reactions under microwave irradiation, including the Diels-Alder reaction [1], Ene reaction [2], Heck reaction [3], Suzuki reaction [4], Mannich reaction [5], as well as hydrogenation of
-lactams [6], hydrolysis [7], dehydration [8], esterification [9], cycloaddition [10], epoxidation [11], reduction [12], condensation [13], and cyclization [14] reactions. Several reactions have been reported in which the