Abstract
This review describes the formation of six-membered heterocyclic compounds and their fused analogues under microwave activation using modern organic transformations including cyclocondensation, cycloaddition, multicomponents and other modular reactions. The review is divided according to the main heterocycle types in order of increasing complexity, starting with heterocyclic systems containing one, two and three heteroatoms and their fused analogues. Recent microwave applications are reviewed, with special focus on the chemistry of bioactive compounds. Selected examples from the 2006 to 2015 literature are discussed.
Highlights
Microwave (MW) irradiation is a technique widely used in organic synthesis, as demonstrated by more than 20 years of success stories
Heterocycle-containing molecules are extensively studied for their synthesis and their applications in medicinal chemistry, and in optics, electronics and material sciences [7,8]
The reaction cascades consisted of an initial Michael addition, tautomerism, intramolecular cyclization, and dehydration leading to aromatization (Scheme 12)
Summary
Microwave (MW) irradiation is a technique widely used in organic synthesis, as demonstrated by more than 20 years of success stories. The reactions were performed under solvent-free conditions using lanthanum oxide as a catalyst This new method pMroolevcuidlees d201th6,e21e,x4p9e2cted products 35 in excellent yields (90%–98%) after short reaction times (40–68o0f s5) in comparison to the classical Hantzsch methods (Scheme 7) [44,45,46]. The reaction cascades consisted of an initial Michael addition, tautomerism, intramolecular cyclization, and dehydration leading to aromatization (Scheme 12) This methodology showed attractive properties, such as short reaction times, high yields and operational activity against Gram-positive (S. aureus and B. subtilis) and Gram-negative (E. coli and S. flexneri) bacteria, and for their antifungal potential against Candida albicans. The catalyst was recovered and reused for the same 11 of 55 reaction during four consecutive runs without any apparent loss of activity
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