Superacidic Cyclization of Activated Anthranilonitriles into 2-Unsubstituted-4-aminoquinolines

4-Aminoquinoline: a comprehensive review of synthetic strategies

4-Aminoquinoline is an important scaffold due to its variety of applications in medicinal, synthetic organic, and industrial chemistry. It has gained great relevance for the development of selective and potent leishmanicidal agents targeting parasite mitochondria, agonists and antagonists of Toll-like receptors (TLRs), antimalarials, and anticancer agents. As a consequence of the importance of 4-aminoquinoline as leishmanicidal, the present mini-review article aims to give comprehensive information about the different synthetic alternatives for the synthesis of 4-aminoquinolines, including (i) reactions based on nucleophilic aromatic substitution via conventional heating, microwave, and ultrasound; (ii) one-pot metal-free or metal-catalyzed reactions of inter- and intramolecular cyclization/annulation; (iii) miscellaneous reactions including the dehydrogenative amination of dihydroquinolin-4(1H)one and amination via Hartwig-Buchwald cross-coupling or rearrangement reactions.

Toward Homogeneous Brønsted-Acid-Catalyzed Intramolecular Carbonyl-Olefin Metathesis Reactions

The carbonyl-olefin metathesis (COM) reaction is an attractive approach for the formation of a new carbon-carbon double bond from a carbonyl precursor. In principle, this reaction can be promoted by the activation of the carbonyl group with a Brønsted acid catalyst; however, it is often complicated as a result of unwanted side reactions under acidic conditions. Thus, there have been only a very few examples of Brønsted-acid-catalyzed COM reactions, all of which required specially designed setups. Herein, we report a new practical homogeneous Brønsted-acid-catalyzed protocol using nitromethane, a readily available solvent, to promote intramolecular ring-closing COM reactions.

Triflic acid-mediated N-heteroannulation of β-anilino-β-(methylthio)acrylonitriles: a facile synthesis of 4-amino-2-(methylthio)quinolines

Various functionalised 4-amino-2-(methylthio)quinolines are synthesised through triflic acid-mediated N-heteroannulation of α-functionalized-β-anilino-β-(methylthio)acrylonitriles for the first time. The N-heteroannulation process is highly chemoselective and has mild reaction conditions. However, this process fails in the absence of the β-methylthio group in the acrylonitriles. In addition, a new double N-heteroannulation process is demonstrated to synthesise indolo[3,2-c]quinolines from non-heterocyclic precursors. Natural product isocryptolepine is synthesised in four steps from an acyclic precursor.

A Consolidated and Continuous Synthesis of Ciprofloxacin from a Vinylogous Cyclopropyl Amide

Ciprofloxacin is a broad-spectrum antibiotic that is recognized as one of the World Health Organization's Essential Medicines. It is particularly effective in the treatment of Gram-negative bacterial infections associated with urinary, respiratory, and gastrointestinal tract infections. A streamlined and high yielding continuous synthesis of ciprofloxacin has been developed, which employs a chemoselective C-acylation step that precludes the need for intermediate isolations, extractions, or purifications. The end-to-end process has a residence time of 4.7 min with a 15.8 g/h throughput at laboratory scale and an overall isolated yield of 83%.

A nickel catalyzed acceptorless dehydrogenative approach to quinolines

A general, efficient and environmentally benign, one-step synthesis of substituted quinoline derivatives was achieved by acceptorless dehydrogenative coupling of o-aminobenzylalcohols with ketones and secondary alcohols catalyzed by a cheap, earth abundant and easy to prepare macrocyclic nickel catalyst [Ni(MeTAA)].