Abstract
The quinoline ring system is one of the most ubiquitous heterocycles in the fields of medicinal and industrial chemistry, forming the scaffold for compounds of great significance. These include anti-inflammatory and antitumor agents, the antimalarial drugs quinine and chloroquine, and organic light-emitting diodes. Quinolines were first synthesized in 1879, and since then a multitude of synthetic routes have been developed. Many of these methods, such as the Skraup, Doebner–Von Miller, and Friedlander quinoline syntheses, are well-known but suffer from inefficiency, harsh reaction conditions, and toxic reagents. This review focuses on recent transition metal-free processes toward these important heterocycles, including both novel routes and modifications to established methods. For example, variations on the Skraup method include microwave irradiation, ionic liquid media, and novel annulation partners, all of which have shown increased reaction efficiency and improved yield of the heteroring-unsubstituted quinoline products. Similarly, modifications to other synthetic routes have been implemented, with the quinoline products displaying a wide variety of substitution patterns.
Highlights
Quinoline was discovered by Runge in 1834 as one of the many components extracted from coal tar [1]
Lewis acid catalysis has featured in recent literature on the Friedländer quinoline synthesis
As with the previously mentioned Skraup and Doebner reactions, the Friedländer quinoline synthesis can be improved by the use of ionic liquids as either solvent or catalyst
Summary
Quinoline was discovered by Runge in 1834 as one of the many components extracted from coal tar [1] While this nitrogen-based heterocycle is not overly useful in and of itself, it is modified with simple to complex functionalities, giving a multitude of compounds that are ubiquitous in the fields of medicinal and industrial chemistry. The prevalence of the quinoline ring system in a vast range of medical and industrial settings can be ascribed mainly to its versatility and broad potential for functionalization It is this versatility which earned it the designation of “privileged scaffold” in medicinal chemistry, a term coined by Evans in 1988 which refers to simple structural subunits present in diverse therapeutic compounds with distinctive receptor affinities [4]. Structures ofI- quinine (I); chloroquine (II); (III), mefloquine iodide (IV); Cl ethyl red(III); and pinacyanol (V)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.