Green Synthetic Approaches for Biologically Relevant Heterocycles

Goutam Brahmachari

• Publisher: Elsevier
• Year: 2014
• eBook ISBN: 9780128005903
• Topic: Physical Sciences
• Subtopic: Organic Chemistry

Green Synthetic Approachesfor Biologically Relevant Heterocycles reviews this significant group of organic compounds within the context of sustainable methods and processes. Each clearly structured chapter features in-depth coverage of various green protocols for the synthesis of a wide variety of bioactive heterocycles classified on the basis of ring-size and/or presence of heteratoms(s). Techniques covered include microwave heating, ultrasound, ionic liquids, solid phase, solvent-free, heterogeneous catalysis, and aqueous media, along with multi-component reaction strategies. This book also integrates advances in green chemistry research into industrial applications and process developments. Green Synthetic Approachesfor Biologically Relevant Heterocycles is an essential resource on green chemistry technologies for academic researchers, R&D professionals, and students working in medicinal, organic, natural product, and agricultural chemistry.- Includes global coverage of a wide variety of green synthetic techniques- Features cutting-edge research in the field of bioactive heterocyclic compounds- Focuses extensively on applications, with numerous examples of biologically relevant heterocycles

Chapter 1

Green Synthetic Approaches for Biologically Relevant Heterocycles

An Overview

Goutam Brahmachari Laboratory of Natural Products & Organic Synthesis, Department of Chemistry, Visva-Bharati (A Central University), West Bengal, India

Abstract

This chapter is aimed to offer an overview of the present book, and summarizes the contents and subject matter of each chapter with an intention to highlight certain glimpses of the coverage to the readers before they go in depth.

Keywords

Biologically relevant heterocycles; Green synthetic approaches; Overview

Outline

1. Introduction 1

2. An Overview of the Book 2

2.1 Chapter 2 2

2.2 Chapter 3 2

2.3 Chapter 4 2

2.4 Chapter 5 2

2.5 Chapter 6 3

2.6 Chapter 7 3

2.7 Chapter 8 3

2.8 Chapter 9 4

2.9 Chapter 10 4

2.10 Chapter 11 4

2.11 Chapter 12 4

2.12 Chapter 13 4

2.13 Chapter 14 5

2.14 Chapter 15 5

2.15 Chapter 16 5

2.16 Chapter 17 5

2.17 Chapter 18 5

2.18 Chapter 19 6

2.19 Chapter 20 6

2.20 Chapter 21 6

3. Concluding Remarks 6

1. Introduction

This book entitled Green Synthetic Approaches for Biologically Relevant Heterocycles is an endeavor to present cutting-edge research developments in environment-friendly strategies and techniques for the synthesis of a wide variety of heterocycles and their functionalized derivatives of medicinal interests and helps the reader understand how green chemistry research continues to make significant contributions in the process developments for heterocyclic motifs, in both laboratory and industrial productions, required for the discovery and development of new medicinal entities. The reference is meant for synthetic chemists, natural product chemists, combinatorial chemists, pharmacologists as well as other practitioners, and advanced students in related fields. The book comprising of 20 technical chapters, features authoritative, thorough, and in-depth discussion on the applications of various green techniques/protocols in the synthesis of biologically relevant heterocycles. The book is also an attempt to integrate advances in green chemistry research into industrial applications and process developments.

This introductory chapter (Chapter 1) presents an overview of the book, and summarizes the contents and subject matter of each chapter so as to offer certain glimpses of the coverage of discussion to the readers before they go for detailed study.

2. An Overview of the Book

The present book contains a total of 20 technical chapters—Chapter 2 to 21; this section summarizes the contents and subject matter of each of these chapters.

2.1. Chapter 2

In Chapter 2, Ranu and his group have illustrated the impact of heterogeneous supported metal catalysts toward the development of green synthetic protocols for nitrogen (N), oxygen (O), and sulfur (S) containing five- and six-membered heterocycles. These heterocyclic scaffolds are of continued interest due to their potent bioactivities and applications as therapeutic drugs. Use of heterogeneous catalysts in organic syntheses has already received considerable attention in both industry and academia due to their environmentally friendly properties—heterogeneous catalysts are usually recoverable from the reaction mixture by simple means and can be reused in subsequent reactions. Moreover, heterogeneous supported metals are found to show superior activity than homogeneous counterparts in many reactions as well. The authors screened a wide variety of heterogeneous supported metals involving transition metals (Pd, Cu, Au, and Sn), bimetallic systems (Pt/Ir and Mg/Al) and metal oxides (PdO, CuO, ZnO, and SnO₂), and described their useful applications with ample of illustrations. Syntheses of five- membered N-containing heterocycles (such as indoles, oxindoles, and triazoles), O-containing heterocycles (such as furans and benzofurans), and S-containing compounds (benzothiazoles and thiophenes) have been considered whereas among six-membered heterocycles, syntheses of quinilones, quinazolines and quinoxalines, benzodioxanes, benzoxazines and 4H-pyrans have been demonstrated under the influence of the said catalytic systems. The preparations of heterogeneous catalysts, their structures, recyclability, and function with reference to certain significant reactions are discussed in detail. In addition, reaction pathways of several reactions are also discussed. The present discussion in Chapter 2 by Ranu and his group would thus be much helpful to the readers at large and must boost the ongoing research in this direction.

2.2. Chapter 3

Chapter 3 by Kaicharla and Biju is devoted to the transition-metal-free synthesis of benzo-fused five and six-membered heterocycles via unique carbon–carbon and carbon–heteroatom bond-forming reactions employing potential arynes. The authors have offered a comprehensive overview of the syntheses of a variety of biologically relevant heterocycles using the potential of arynes under green and operationally simple procedures. The versatile transition-metal-free applications of arynes include cycloaddition reactions, insertion reactions, and multicomponent reactions for the construction of various heterocycles. As discussed in the present chapter about the advantages of using the aryne route to heterocycles include the synthesis under transition-metal-free conditions, use of cheap and readily available starting materials, the rapid construction of heterocycles in one-step or in one-pot, excellent levels of selectivity, and a broad range of applicability. This illuminating review on arynes chemistry would obviously enrich the readers with these synthetically and biologically useful molecules and also would attract the attention of researchers working in this area.

2.3. Chapter 4

In Chapter 4, Cadierno has offered an update on the metal-catalyzed routes for the synthesis of furocoumarins and coumestans. These scaffolds represent a relevant family of heterocyclic compounds of natural origin with a wide range of biological activities, and are currently of great interest for medicinal applications. Spurred by the principles of green chemistry, chemists at large have now been motivated to develop more selective, economical, and cleaner synthetic transformations. Metal-catalyzed transformations are found to provide the most appealing methodologies to access furocoumarin and coumestan scaffolds in an efficient and atom-economical manner. Throughout this chapter, the author has illustrated the enormous potential of the metal-based approaches for the construction of these heterocycles of biological interest. This field remains open, and the present discussion would boost the ongoing research for new discoveries in this area of interest in the coming years.

2.4. Chapter 5

Dolzhenko and Dolzhenko have presented a comprehensive review on the use of green solvents for eco-friendly synthesis of bioactive heterocyclic compounds in Chapter 5. Use of safer solvents is considered as one of the most significant criteria in green chemistry practice. In the synthesis of biologically active compounds with the aim to improve public health, it is extremely important to minimize impact of this process on the health and nature by choosing solvents, which are nontoxic, easily and completely biodegradable. This chapter is dedicated to the synthesis of heterocyclic compounds of potential medicinal interest using supercritical carbon dioxide and unconventional eco-friendly solvents with good biodegradability property, such as polyethylene glycols (PEGs) and some bio-derived solvents (glycerol, ethyl lactate, and gluconic acid aqueous solution). These reaction media have enormous potential for use in medicinal chemistry with many advantages over conventional organic solvents. It is to be mentioned that the search for new green solvents should ultimately be based on their origin from renewable sources. This overview would surely help the researchers a lot deeply involved in the synthesis of heterocycles using green solvents from supercritical CO₂ to PEGs and bio-based solvents.

2.5. Chapter 6

Kleij has provided a comprehensive review on green catalytic synthesis of heterocyclic structures using carbon dioxide and related motifs in Chapter 6. The synthesis of heterocyclic compounds constructed by coupling of carbon dioxide with various reaction partners has recently undergone considerable advancement over the last five years; hence, there are currently a number of relatively green methodologies available for the synthesis of pharmaceutically relevant structures including 1,3-dioxolan-2-ones and 1,3-dioxan-2-ones (cyclic carbonates) and oxazolidinones/oxazodinanones (cyclic carbamates). This carbon source may be regarded as a renewable feed stock having a number of interesting features including cheapness, availability, and low toxicity. Current challenges for its conversion have driven contemporary chemists to design new and improved catalytic strategies that can address the need for cleaner production of a range of base chemicals using renewable sources. The present chapter would boost the ongoing advancement in this remarkable field of research, and motivate the young researchers in this direction.

2.6. Chapter 7

Chapter 7 deals with an update on the formation of three- to seven-membered aza-heterocycles in aqueous media using conventional thermal energy or other energy sources such as microwave and ultrasonic irradiation by Singh and Tabane. The application of “on water” organic chemistry in synthesis of aza-heterocyclic compounds has seen a tremendous development in recent years. Water is undoubtedly the cheapest, most abundant, and environmentally benign solvent. Syntheses of highly reactive small-ring heterocycles like aziridine, azetidines, and 2-azetidinones have been discussed elaborately in aqueous media. Besides, most of the common reactions for synthesis of pyrroles, benzimidazoles, indoles, pyridines, and pyrimidines have been revisited using water as solvent. Among seven-membered rings, formation of azulenone and oxoazepan rings is described by appropriate multicomponent reactions. T...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Contributors
• About the Editor
• Foreword
• Preface
• Chapter 1. Green Synthetic Approaches for Biologically Relevant Heterocycles: An Overview
• Chapter 2. Synthesis of Bioactive Five- and Six-Membered Heterocycles Catalyzed by Heterogeneous Supported Metals
• Chapter 3. Transition-Metal-Free Synthesis of Benzo-Fused Five- and Six-Membered Heterocycles Employing Arynes
• Chapter 4. Metal-Catalyzed Routes for the Synthesis of Furocoumarins and Coumestans
• Chapter 5. Green Solvents for Eco-friendly Synthesis of Bioactive Heterocyclic Compounds
• Chapter 6. Green Catalytic Synthesis of Heterocyclic Structures Using Carbon Dioxide and Related Motifs
• Chapter 7. Synthetic Approaches to Small- and Medium-Size Aza-Heterocycles in Aqueous Media
• Chapter 8. Green Synthetic Approaches for Biologically Relevant 2-amino-4H-pyrans and 2-amino-4H-pyran-Annulated Heterocycles in Aqueous Media
• Chapter 9. Sustainable Synthesis of Benzimidazoles, Quinoxalines, and Congeners
• Chapter 10. Green and Catalytic Methods for γ-Lactone Synthesis
• Chapter 11. Green Synthetic Approaches for Medium Ring-Sized Heterocycles of Biological Interest
• Chapter 12. Organocatalyzed Biginelli Reactions: A Greener Chemical Approach for the Synthesis of Biologically Active 3,4-Dihydropyrimidin-2(1H)-ones/-thiones
• Chapter 13. Photocatalytic Minisci Reaction: A Promising and Eco-friendly Route to Functionalize Heteroaromatics of Biological Interest
• Chapter 14. Organohypervalent Iodine Reagents in the Synthesis of Bioactive Heterocycles
• Chapter 15. Porous Catalytic Systems in the Synthesis of Bioactive Heterocycles and Related Compounds
• Chapter 16. High-Pressure Cycloaddition Reactions in the Synthesis of Biologically Relevant Heterocycles
• Chapter 17. Ionic Liquids-Prompted Synthesis of Biologically Relevant Five- and Six-Membered Heterocyclic Skeletons: An Update
• Chapter 18. Heterocycles-Based Ionic Liquid-Supported Synthesis of Small Organic Molecules
• Chapter 19. Microwave-Induced Synthesis of Heterocycles of Medicinal Interests
• Chapter 20. Application of Microwave Irradiation in the Synthesis of P-Heterocycles
• Chapter 21. Use of Ultrasound in the Synthesis of Heterocycles of Medicinal Interest
• Index