Combining Organometallic Reagents, the Sulfur Dioxide Surrogate DABSO, and Amines: A One-Pot Preparation of Sulfonamides, Amenable to Array Synthesis

A Sulfoxide Reagent for One-Pot, Three-Component Syntheses of Sulfoxides and Sulfinamides

Sulfoxides and sulfinamides represent versatile sulfur functional groups found in ligands, chiral auxiliaries, and bioactive molecules. Canonical two-component syntheses, however, rely on substrates with a preinstalled C-S bond and impede efficient and modular access to these sulfur motifs. Herein is presented the application of an easily prepared, bench-stable sulfoxide reagent for one-pot, three-component syntheses of sulfoxides and sulfinamides. The sulfoxide reagent donates the SO unit upon the reaction with a Grignard reagent (RMgX) as a sulfenate anion (RSO- ). While subsequent trapping reactions of this key intermediate with carbon electrophiles provide sulfoxides, a range of tertiary, secondary, and primary sulfinamides can be prepared by substitution reactions with electrophilic amines. The syntheses of sulfinamide analogs of amide- and sulfonamide-containing drugs illustrate the utility of the method for the rapid preparation of medicinally relevant molecules.

An Efficient Method for the Preparation of Sulfonamides from Sodium Sulfinates and Amines

Sulfonamides have a special role on medicine due to their broad biological activities, as bacterial infections, diabetes mellitus, oedema, hypertension prevention and treatment. In addition, sulfonamides are also useful in herbicides and pesticides. Herein, we communicate an efficient strategy for the preparation of sulfonamides via NH₄I‐mediated amination of sodium sulfinates. This new method provides a general and environmentally friendly access to sulfonamide compounds and tolerates a wide range of functional groups.

Carboxylic Acid Bioisosteres in Medicinal Chemistry: Synthesis and Properties

Lead optimization represents the tedious process of fine-tuning lead compounds from biologically active hits to suitable drug candidates for clinical trials. By chemically modifying a hit structure, an improved compound can be obtained in terms of activity, selectivity, and pharmacokinetic ADME (absorption, distribution, metabolism, and excretion) properties. The carboxylic acid moiety is known to be a crucial functionality in many pharmaceutically active compounds. Despite its common use as a key functionality in drugs, its presence in a lead molecule is often associated with poor pharmacokinetic properties and toxicity. In this literature overview, we discuss how the shortcomings of a carboxylic acid can be circumvented by replacing this functionality with bioisosteres. In this way, the positive aspects of this moiety, such as its activity, for example, by virtue of its capacity to form hydrogen bonds, can be maintained or even improved. To that end, we provide an overview of the most promising carboxylic acid bioisosteres and discuss a selection of synthetic routes towards the main functionalities.

Expeditious and Efficient ortho-Selective Trifluoromethane-sulfonylation of Arylhydroxylamines

A metal- and oxidant-free, practical and efficient method for the synthesis of highly versatile and synthetically useful ortho-trifluoromethanesulfonylated anilines from arylhydroxylamines and trifluoromethanesulfinic chloride was developed. This rapid transformation proceeded smoothly with good yields and excellent ortho-selectivity in the absence of any metals or ligands. Mechanistically, the reaction comprised a noncanonical O-trifluoromethanesulfinylation of the arylhydroxylamine, and the subsequent [2,3]-sigmatropic rearrangement to afford ortho-trifluoromethanesulfonylated aniline derivatives. The practical application of this reaction was demonstrated by further conversion into a series of functional molecules under different reaction conditions.

A Broad-Spectrum Catalytic Amidation of Sulfonyl Fluorides and Fluorosulfates*

A broad-spectrum, catalytic method has been developed for the synthesis of sulfonamides and sulfamates. With the activation by the combination of a catalytic amount of 1-hydroxybenzotriazole (HOBt) and silicon additives, amidations of sulfonyl fluorides and fluorosulfates proceeded smoothly and excellent yields were generally obtained (87-99 %). Noticeably, this protocol is particularly efficient for sterically hindered substrates. Catalyst loading is generally low and only 0.02 mol % of catalyst is required for the multidecagram-scale synthesis of an amantadine derivative. In addition, the potential of this method in medicinal chemistry has been demonstrated by the synthesis of the marketed drug Fedratinib via a key intermediate sulfonyl fluoride 13. Since a large number of amines are commercially available, this route provides a facile entry to access Fedratinib analogues for biological screening.

Sodium Dithionite-Mediated Decarboxylative Sulfonylation: Facile Access to Tertiary Sulfones

A straightforward multicomponent decarboxylative cross coupling of redox-active esters (N-hydroxyphthalimide ester), sodium dithionite, and electrophiles was established to construct sterically bulky sulfones. The inorganic salt sodium dithionite not only served as the sulfur dioxide source, but also acted as an efficient radical initiator for the decarboxylation. Notably, diverse naturally abundant carboxylic acids and artificially prepared carboxyl-containing drugs with multiple heteroatoms and sensitive functional groups successfully underwent this decarboxylative sulfonylation to provide sterically bulky tertiary sulfones. Mechanistic studies further demonstrated that decarboxylation was the rate-determining step and occurred via a single-electron transfer (SET) process with the assistance of sodium dithionite.

Cyclic Alkenylsulfonyl Fluorides: Palladium-Catalyzed Synthesis and Functionalization of Compact Multifunctional Reagents

A series of low‐molecular‐weight, compact, and multifunctional cyclic alkenylsulfonyl fluorides were efficiently prepared from the corresponding alkenyl triflates. Palladium‐catalyzed sulfur dioxide insertion using the surrogate reagent DABSO effects sulfinate formation, before trapping with an F electrophile delivers the sulfonyl fluorides. A broad range of functional groups are tolerated, and a correspondingly large collection of derivatization reactions are possible on the products, including substitution at sulfur, conjugate addition, and N‐functionalization. Together, these attributes suggest that this method could find new applications in chemical biology.

Selective Late-Stage Sulfonyl Chloride Formation from Sulfonamides Enabled by Pyry-BF4

Reported here is a simple and practical functionalization of primary sulfonamides, by means of a pyrylium salt (Pyry‐BF₄), with nucleophiles. This simple reagent activates the poorly nucleophilic NH₂ group in a sulfonamide, enabling the formation of one of the best electrophiles in organic synthesis: a sulfonyl chloride. Because of the variety of primary sulfonamides in pharmaceutical contexts, special attention has been focused on the direct conversion of densely functionalized primary sulfonamides by a late‐stage formation of the corresponding sulfonyl chloride. A variety of nucleophiles could be engaged in this transformation, thus permitting the synthesis of complex sulfonamides, sulfonates, sulfides, sulfonyl fluorides, and sulfonic acids. The mild reaction conditions and the high selectivity of Pyry‐BF₄ towards NH₂ groups permit the formation of sulfonyl chlorides in a late‐stage fashion, tolerating a preponderance of sensitive functionalities.

Cross-Coupling of Sodium Sulfinates with Aryl, Heteroaryl, and Vinyl Halides by Nickel/Photoredox Dual Catalysis

An efficient photoredox/nickel catalyzed sulfonylation reaction of aryl, heteroaryl, and vinyl halides has been achieved for the first time. This newly developed sulfonylation protocol provides a versatile method for the synthesis of diverse aromatic sulfones at room temperature and shows excellent functional group tolerance. The electrophilic coupling partners are not limited to aryl, heteroaryl, and vinyl bromides and iodides, but also includes less reactive aryl chlorides as suitable substrates for this transformation.

One-Pot Bimetallic Pd/Cu-Catalyzed Synthesis of Sulfonamides from Boronic Acids, DABSO and O-Benzoyl Hydroxylamines

A practical and straightforward bimetallic Pd/Cu catalytic system has been developed. This system affords various sulfonamides in one pot from easy-to-handle and readily available boronic acids, sulfur dioxide surrogate DABSO and O-benzoyl hydroxylamines in high yields. Without additional ligands, the newly developed catalytic system revealed a broad substrate scope for both partners and tolerated a wide array of functional groups even at low catalyst loadings. Furthermore, based on control experiments, a plausible mechanism has been proposed, in which sodium sulfinate has been isolated and identified as the crucial intermediate for this transformation.

Evaluating New Chemistry to Drive Molecular Discovery: Fit for Purpose?

As our understanding of the impact of specific molecular properties on applications in discovery-based disciplines improves, the extent to which published synthetic methods meet (or do not meet) desirable criteria is ever clearer. Herein, we show how the application of simple (and in many cases freely available) computational tools can be used to develop a semiquantitative understanding of the potential of new methods to support molecular discovery. This analysis can, among other things, inform the design of improved substrate scoping studies; direct the prioritization of specific exemplar structures for synthesis; and substantiate claims of potential future applications for new methods.

Palladium(II)-Catalyzed Synthesis of Sulfinates from Boronic Acids and DABSO: A Redox-Neutral, Phosphine-Free Transformation

A redox-neutral palladium(II)-catalyzed conversion of aryl, heteroaryl, and alkenyl boronic acids into sulfinate intermediates, and onwards to sulfones and sulfonamides, has been realized. A simple Pd(OAc)2 catalyst, in combination with the sulfur dioxide surrogate 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) (DABSO), is sufficient to achieve rapid and high-yielding conversion of the boronic acids into the corresponding sulfinates. Addition of C- or N-based electrophiles then allows conversion into sulfones and sulfonamides, respectively, in a one-pot, two-step process.