Phosphonium Salt-Promoted C2-H Functionalization of Heterocyclic N-Oxides

Synthesis of quinoline mimics via C-H bond functionalization of quinoline: a review on recent progress

Functionalization of the quinoline ring has emerged as a transformative strategy in modern synthetic chemistry because of the medicinal potential of quinoline-based scaffolds. The precise and selective introduction of diverse functional groups significantly expands the chemical space and enhances the pharmacological profile of quinoline derivatives. By carefully selecting catalysts, reaction conditions, and directing groups, researchers have unlocked novel pathways for the efficient synthesis of quinoline-based compounds with improved efficacy, target selectivity, and safety. This approach accelerates drug discovery and broadens the therapeutic potential of quinoline scaffolds for treating various diseases, including cancer, infectious diseases, and neurological disorders. Over the past two decades, this field has experienced exponential growth, as evidenced by the increasing number of research publications and comprehensive review articles. This surge in interest is driven by the potential of quinoline functionalization to generate novel drug candidates with enhanced bioactivity and reduced side effects. This review summarizes the key advancements from January 2021 to 2024, focusing on the latest methodologies, catalytic systems, and applications in drug development.

Direct C3-H Alkylation and Alkenylation of Quinolines with Enones

Conversion of quinoline C-H bonds into C-C bonds is essential for obtaining the enormous array of derivatives required for pharmaceutical and agrochemical development. Despite over a century of synthetic efforts, direct alkylation and alkenylation at C3-H positions in a wide array of quinoline precursors remain predominantly challenging and elusive. This report outlines the first successful quinoline C3-H alkylation and alkenylation reactions, exhibiting exceptional regio- and stereoselectivity, all achieved under redox-neutral and transition-metal-free conditions. The method involves a three-step, one-pot or two-pot sequence, including 1,4-dearomative addition, functionalization at C3, and elimination or transalkylation to produce 3-alkylated/alkenylated quinolines. The presence of a carbonyl group in these products allows for further synthetic manipulations, enabling the production of cyanides, amides, amines, and simple alkyl derivatives.

Accessing 1,8-Naphthyridone-3-carboxylic Acid Derivatives and Application to the Synthesis of Amfonelic Acid

1,8-Naphthyridone-3-carboxyl is the core structure of several on-market antibacterial drugs. It has prompted significant interest from the synthetic community. Here, we report a practical synthesis of diversely functionalized 1,8-naphthyridone-3-carboxylic acid derivatives starting from readily available and inexpensive nicotinic acid derivatives. All key steps have been optimized. Furthermore, the usefulness of this protocol has been exemplified by the first synthesis of amfonelic acid.