1-Butyl-3-methylimidazolium Hydrogen Sulfate ([bmim]-HSO4)–Mediated Synthesis of Polysubstituted Quinolines

Microwave-assisted, [Bmim]HSO4-catalyzed the Friedländer quinoline synthesis of quinoline under solvent-free conditions

Abstact:

An efficient and green method for the Friedländer quinoline synthesis is described. The synthesis was performed under microwave irradiation using ionic liquid [Bmim]HSO4 as a catalyst. A diverse range of quinoline derivatives was obtained in high yields from 2‐aminoaryl aldehydes and ketones under solvent-free conditions.

Organocatalyzed Synthesis of Functionalized Quinolines

As one of the most widely investigated compound skeleton, quinolines possess important medicinal and biological activities. As such, a great number of literatures, including reviews, have reported various methodologies to construct quinolines. Recently, organocatalyzed reactions have attracted the attention of organic chemists due to its being "green" because the reactions avoid the use of toxic metals. In this review, various distinctive contributions are surveyed with specific emphasis on organocatalyzed reactions for quinoline core constructions.

Recent Advances in Metal-Free Quinoline Synthesis

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.

Palladium-catalyzed synthesis of polysubstituted quinolines from 2-amino aromatic ketones and alkynes

A palladium-catalyzed one-pot method for the synthesis of quinolines from commercial or readily available 2-amino aromatic ketones and alkynes is reported for the first time.