Recent Advancements in Pyrrole Synthesis

This review article features selected examples on the synthesis of functionalized pyrroles that were reported between 2014 and 2019. Pyrrole is an important nitrogen-containing aromatic heterocycle that can be found in numerous compounds of biological and material significance. Given its vast importance, pyrrole continues to be an attractive target for the development of new synthetic reactions. The contents of this article are organized by the starting materials, which can be broadly classified into four different types: substrates bearing π-systems, substrates bearing carbonyl and other polar groups, and substrates bearing heterocyclic motifs. Brief discussions on plausible reaction mechanisms for most transformations are also presented.

Microwave assisted synthesis of five membered nitrogen heterocycles

Our continuously changing environment demands sensible and sustainable chemistry. Consequently, organic synthesis started to follow green chemistry principles in recent years. It is observed that microwave (MW) radiation has been widely used as a source of energy in organic synthesis in the past decade. The MW heating approach has evolved into a new green method in organic synthesis since it provides short reaction time, high yields, and high product purities along with a decrease in the rate of by-product formation. Solvent-free reaction protocols worked well under MW irradiation. All these features make MW assisted organic synthesis an environment-friendly approach. In organic synthesis, heterocycles are vital targets especially nitrogen-containing ones because of their prominent presence in natural products and widespread applications in pharmaceutical industries. Five membered nitrogen heterocycles include pyrroles, oxazoles, pyrrolidones, etc. among which pyrroles are the most important ones due to their potent biological properties. Even though there are a variety of reaction protocols for the synthesis of pyrroles, a significant development materialized in MW assisted synthesis of pyrroles in the past few years. In this review, we focus on the developments in MW assisted synthesis of pyrroles and other five-membered nitrogen heterocycles.

Recent Progress in the Synthesis of Pyrroles

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Pyrrole derivatives are nitrogen-containing heterocyclic compounds and widely distributed in a large number of natural and non-natural compounds. These compounds possess a broad spectrum of biological activities such as anti-infammatory, antiviral, antitumor, antifungal, and antibacterial activities. Besides their biological activity, pyrrole derivatives have also been applied in various areas such as dyes, conducting polymers, organic semiconductors.

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Due to such a wide range of applicability, access to this class of compounds has attracted intensive research interest. Various established synthetic methods such as Paal-Knorr, Huisgen, and Hantzsch have been modified and improved. In addition, numerous novel methods for pyrrole synthesis have been discovered. This review will focus on considerable studies on the synthesis of pyrroles, which date back from 2014.