Synthesis of Highly Reactive Sulfone Iminium Fluorides and Their Use in Deoxyfluorination and Sulfur Fluoride Exchange Chemistry

Recent Advances in Fluorination Reactions via De-Carboxylative and De-Oxygenative Strategies: A Perspective

Organic fluorine compounds encompass a vast and diverse variety of species that possess unique biological activity due to the presence of fluorine atoms. Fluorine is highly electronegative, increases the lipophilicity (fat-solubility) and hydrophobicity (water-repellent nature) of molecules, often exhibit remarkable chemical and thermal stability. This is especially useful in drug design, as it can improve the bioavailability of pharmaceutical compounds and help them interact more effectively with biological membranes. The growing demand for fluorinated compounds in materials science, agrochemicals, and medicine has made selective fluorine incorporation into organic molecules a challenging but necessary component of modern organic synthesis. Development of C-F building blocks are invaluable in organic synthesis due to their ability to impart chemical stability, selectivity, and reactivity to organic molecules. This article provides a detailed analysis of two popular fluorination processes: deoxyfluorination and decarboxyfluorination. Deoxyfluorination is the process of enhancing the physicochemical properties of molecules by replacing hydroxyl groups with fluorine atoms. Decarboxyfluorination is a type of chemical reaction where transformation of carboxylic acid derivatives into fluorinated compounds. The various fluorinating reagents, mechanistic processes, synthetic uses and substrate scope are covered in this section. When combined, these novel transformation strategies provide effective and focused approaches to the production of C-F bonds, offering useful resources for obtaining fluorinated compounds. This review mainly focuses on the construction of fluorinated compounds via deoxygenative and decarboxylative fluorination since 2011. We hope this review offers a useful conceptual overview and inspires further advancements in the efficient construction of C-F bond.

Palladium-Catalyzed Addition of Aryl Halides to N-Sulfinylamines for the Synthesis of Sulfinamides

Sulfinamides are versatile, synthetically useful intermediates, and final motifs. Traditional methods to synthesize sulfinamides generally require substrates with preinstalled sulfur centers. However, these precursors have limited commercial availability, and the associated synthetic routes often require harsh reaction conditions and highly reactive reagents, thus severely limiting their application. Herein, we report the synthesis of sulfinamides from aryl and alkenyl (pseudo)halides and N-sulfinylamines, enabled by palladium catalysis. The reactions use mild conditions and are achieved without the use of highly reactive preformed organometallic reagents, resulting in transformations of broad generality and high functional group tolerance. In particular, substrates featuring protic and electrophilic functional groups can be used successfully. The modification of complex aryl cores and natural product derivatives demonstrates the utility of this method.

Deoxyfluorination of Carboxylic Acids via an In Situ Generated Trifluoromethoxide Salt

An in situ generated pyridinium trifluoromethoxide salt (PyOCF3) is a highly effective deoxyfluorination reagent for the synthesis of acid fluorides. PyOCF3 is formed at room temperature from the reaction of 2,4-dinitro(trifluoromethoxy)benzene with 4-dimethylaminopyridine. PyOCF3 undergoes slow release of fluorophosgene and fluoride, which serve as the electrophile and nucleophile, respectively, for deoxyfluorination. A wide substrate scope and high functional group tolerance are demonstrated. Furthermore, the acid fluorides can be purified by filtration and telescoped to various known reactions.

Soft Fluorination of 4-Alkylpyridines

We report the mild and selective mono- and difluorination of 4-alkylpyridines. The process involves soft-dearomatization of pyridines to the corresponding alkylidene dihydropyridines and treatment with Selectfluor. The reaction tolerates a broad range of functional groups, including those bearing acidic and weak C-H bonds. In addition, selective fluorination of 4-alkylpyridines attached to 2-alkylpyridines and 2-alkylpyrimidines can be achieved in good yields, but a 4-alkylpyridine tethered to a 4-alkylpyrimidine is fluorinated at both heterobenzylic positions.

A modified Beckmann rearrangement for the facile synthesis of amidines and imidates via imidoyl fluoride intermediates

Herein, we report a modified Beckmann rearrangement using sulfone iminium fluoride (SIF) reagents to rapidly synthesize imidoyl fluoride intermediates. Subsequently, amidine and imidate products can be formed following the introduction of amine and alcohol nucleophiles, respectively. Overall, approximately 50 amidine and imidate products have been isolated in high yields utilizing mild conditions.

Rapid Generation of P(V)-F Bonds Through the Use of Sulfone Iminium Fluoride Reagents

Phosphorus-fluorine bonds have become increasingly relevant in the pharmaceutical industry. To continue their exploration, more efficient synthetic methods are needed. Here, we report the application of sulfone iminium fluoride (SIF) reagents to the synthesis of P(V)-F bonds. The SIF reagents promote the deoxyfluorination of phosphinic acids in just 60 s with excellent yields and scope. The same P(V)-F products can also be synthesized from secondary phosphine oxides using an SIF reagent.