Recent synthetic journey on pyrrole-fused compounds

Abstract

Pyrroles and their fused compounds are widely known as biologically active scaffolds, which are mainly fused at the 1–2 (a), 2–3 (b), 3–4 (c) and 4–5 (d) positions. In pyrrole ring systems, the combination of ring fusions (a–b/a–c/a–d, etc.) gives rise to pharmacophores, resulting in the production of more active molecules. In this tutorial review, we highlight the recent research on the synthesis of different pyrrole-fused heterocycles. Specifically, we categorize the fused pyrroles according to their site of fusion and highlight their various applications in pharmacology, materials science, industry, and biological science. Furthermore, we present the diverse synthetic methods reported for the production of the pyrrole ring by modification of the existing synthetic pathways, metal/metal-free approaches for the synthesis of a-, b- and c-fused rings, multi-step reactions, and cascade reactions for multi-fused rings. This review aims to provide readers with broad knowledge on the synthesis and relevance of diverse fused pyrrole rings, which are considered to be particularly relevant to the disciplines of synthetic chemistry, medicinal chemistry, and drug development.