Sulfonimidamides in Medicinal and Agricultural Chemistry

The synthesis and evaluation of structural analogues and isosteres are of central importance in medicinal and agricultural chemistry. The sulfonamide functional group represents one of the most important amide isosteres in contemporary drug design, and about 500 such compounds have overcome both the pharmacological and regulatory hurdles that precede studies in humans. The mono aza analogues of sulfonamides, that is, sulfonimidamides, are rapidly gaining popularity as a novel functional group among synthetic chemists involved in the design of biologically active compounds for both pharmaceutical and agrochemical applications. Herein, we review these recent developments to showcase the promise of this functional group.     

Sulfonimidamides and Imidosulfuric Diamides: Compounds from an Underexplored Part of Biologically Relevant Chemical Space

Two novel solid reagents—1-sulfonimidoyl- and 1-sulfamimidoyl-3-methylimidazolium derivatives—for the synthesis of sulfonimidamides and imidosulfuric diamides, respectively, were developed. It is shown that these reagents are very effective in substitution reactions with various N- and O-nucleophiles; therefore, they significantly extend the accessibility to the chemical space covered by organosulfur(VI) compounds with S=N bonds. In addition, previously unknown imidosulfuric diamides with free imino nitrogen groups were prepared, and their physical and chemical properties were characterized (including molecular geometry, pK_a, Log P, microsomal stability, and reactivity towards typical electrophiles). Similar to other organosulfur(VI) derivatives with S=N bonds, these compounds can be considered as promising bioisosteres of amides, ureas, or sulfonamides.     

Synthesis of Highly Enantioenriched Sulfonimidoyl Fluorides and Sulfonimidamides by Stereospecific Sulfur–Fluorine Exchange (SuFEx) Reaction

Sulfonimidamides present exciting opportunities as chiral isosteres of sulfonamides, with potential for additional directional interactions. Here, we present the first modular enantioselective synthesis of sulfonimidamides, including the first stereoselective synthesis of enantioenriched sulfonimidoyl fluorides, and studies on their reactivity. A new route to sulfonimidoyl fluorides is presented from solid bench-stable, N-Boc-sulfinamide (Boc=tert-butyloxycarbonyl) salt building blocks. Enantioenriched arylsulfonimidoyl fluorides are shown to be readily racemised by fluoride ions. Conditions are developed, which trap fluoride and enable the stereospecific reaction of sulfonimidoyl fluorides with primary and secondary amines (100 % es, es=enantiospecificity) generating sulfonimidamides with up to 99 % ee. Aryl and alkyl sulfonimidoyl fluoride reagents are suitable for mild late stage functionalisation reactions, exemplified by coupling with a selection of complex amines in marketed drugs.     

Catalyst-Controlled Dual Reactivity of Sulfonimidamides: Synthesis of Propargylamines and N-Propargyl Sulfonimidamides

Sulfonimidamides (SIAs) are acting both as surrogate amines and nucleophiles depending on the reaction conditions to access propargylamines and N-propargyl SIAs, respectively. The amine part of SIAs has been cleaved in an InCl₃-catalyzed three-component A³ coupling reaction with aldehyde and acetylene to yield propargylamine. Moreover, N-propargyl SIAs were obtained via the direct-imination of propargyl alcohols in the presence of BF₃⋅OEt₂.     

3D Heterocycles from Sulfonimidamides by Sequential C−H Bond Alkenylation/Aza-Michael Cyclization

Starting from NH-sulfonimidamides, rhodium-catalyzed C−H bond alkenylation followed by aza-Michael cyclization leads to unprecedented benzoisothiazole 1-oxides. The applicability and robustness of the method is demonstrated in 25 examples with yields up to 95 %. The resulting scaffolds are partly saturated, 3D heterocycles with potential significance for medicinal and agricultural chemistry.     

One‐Pot,Three‐Component Sulfonimidamide Synthesis Exploiting the Sulfinylamine Reagent N‐Sulfinyltritylamine,TrNSO

Sulfonimidamides are increasingly important molecules in medicinal chemistry and agrochemistry, but their preparation requires lengthy synthetic sequences, which has likely limited their use. We describe a one‐pot de novo synthesis of sulfonimidamides from widely available organometallic reagents and amines. This convenient and efficient process uses a stable sulfinylamine reagent, N‐sulfinyltritylamine (TrNSO), available in one step on 10 gram scale, as a linchpin. In contrast to classical approaches starting from thiols or their derivatives, our TrNSO‐based approach facilitates the rapid assembly of the three reaction components into a variety of differentially substituted sulfonimidamides containing medicinally relevant moieties, including pyridines and indoles. Analogues of the sulfonamide‐containing COX‐2 inhibitor Celecoxib were prepared and evaluated.     

Copper‐Catalyzed S−C/S−N Bond Interconversions

Under an atmosphere of dioxygen, copper‐catalyzed de‐alkylation/amination sequences provide sulfonimidamides from unprotected sulfoximines in moderate to good yields. Mechanistic studies suggest the involvement of radicals in both the C?S bond cleavage and the formation of the new N?S bond.     

Rediscovering Sulfinylamines as Reagents for Organic Synthesis

Sulfinylamines (R−N=S=O), monoaza analogues of sulfur dioxide, have been known for well over a century, and their reactivity as sulfur electrophiles and in Diels-Alder reactions is well-established. However, they have only rarely been used in organic synthesis in recent decades despite the increasing prominence of compounds containing N=S=O functionality, such as sulfoximines and sulfonimidamides. This Minireview aims to bring wider visibility to the unique chemistry enabled by this class of compounds. We focus on advances from the last 10 years, including the first examples of their use in the one-pot syntheses of sulfoximines and sulfonimidamides. Also covered are the reactions of sulfinylamines with carbon-centred radicals, their use for formation of heterocycles through cycloadditions, and catalytic enantioselective allylic oxidation of alkenes via a hetero-ene reaction. These examples highlight the different reactivity modes of sulfinylamines and their underappreciated potential for forming molecules which contain high- or low-valent sulfur, or even no sulfur at all.