Synthesis of Sulfinamidines and Sulfinimidate Esters by Transfer of Nitrogen to Sulfenamides

Azasulfur(iv) derivatives of sulfite and sulfinate esters by formal S-S bond insertion of dichloramines

Azasulfur(vi) compounds such as sulfoximines and sulfonimidamides are attractive due to the unique properties of the S[double bond, length as m-dash]N bond. While the synthesis of these carbon-attached sulfonimidoyl derivatives is well-established, the situation is different for their heteroatom-bound counterparts. In this work, we propose azasulfur(iv) esters as platform chemicals that can be derivatized to obtain all types of SVI[double bond, length as m-dash]N functional groups, among these are the poorly accessible, all-heteroatom imidosulfate esters. Using a chloroamination workflow established here, S-S bond-containing structures such as elemental sulfur or diaryl disulfides can be transformed into imidothionyl or sulfinimidoyl chlorides, which are easily esterified or amidated. Thus, chloramines serve as a versatile [N] and [Cl+] source, and by using them in the context reported here, we advance the set of mild synthetic methods as the latest toolbox member to cover even more of the azasulfur(iv) and (vi) chemical space.

Copper-Catalyzed Aerobic S-Amination of Sulfenamides for the Synthesis of Sulfinamidines

Herein, we present a copper-catalyzed oxidative amination of sulfenamides for the synthesis of sulfinamidines. By the employment of air as the terminal oxidant, a diverse array of secondary and primary amines can be efficiently transformed into their corresponding products. This method is well-suited for last-stage functionalization, and the underlying mechanism has been investigated. The transformation is characterized by exceptional chemoselectivity, mild conditions, facile operation, and broad substrate compatibility, which have significant implications for the fields of pharmaceuticals and organic synthesis.

Anomeric Answer to Sulfenamide Stability and α-Nucleophilicity

The S-N bond remains a synthetically challenging motif for organic chemists to access. The problem arises from instability in many sulfenamide derivatives, which has led to fewer S-N bond surrogate molecules compared to their hydroxylamine (NH2OH) and hydrazine (NH2NH2) analogues. In turn, sulfenamides have often been omitted in studies regarding α-nucleophilicity. Herein, we provide factors responsible for the stability of the sulfenamide motif and provide new insights on the nucleophilic properties of sulfenamides as they relate to the α-effect.

Overlooked aza-S(IV) motifs: synthesis and transformations of sulfinamidines and sulfinimidate esters

Significant advancements have been made in the synthesis of overlooked aza-S(IV) motifs. The accessibility of sulfinamidines and sulfinimidate esters has greatly improved through the recent development of efficient and complementary synthetic strategies. Intriguingly, new discoveries have emerged regarding the reactivity of these substances, highlighting the electrophilic nature of sulfinimidate esters and the nucleophilic character of sulfinamidines. Moreover, sulfinamidines have been found to be prone to oxidation, leading to the formation of important aza-S(VI) derivatives. In this review, our aim is to present an almost comprehensive overview of the most relevant achievements in the preparation and structural characterization of these overlooked compounds.

Silver-Catalyzed para-Selective Sulfenyl Group Transfer Reactions of N-Sulfenylanilides

Silver-catalyzed reactions of N-sulfenylanilides afforded the corresponding p-sulfenylanilides in good to high yields with good para selectivity. The transformation has a high compatibility of functional groups, such as ester, bromo, and iodo groups. Mechanistic studies indicate that the rearrangement reaction proceeds through intermolecular transfer of the sulfenyl group.

Hypervalent Iodine Mediated Synthesis of Sulfinamidines from Sulfenamides

In this study, we present a novel, efficient method for the oxidative amination of sulfenamides using diacetoxyiodobenzene (PhI(OAc)2) and amines under basic conditions. This innovative technique streamlines the synthesis of sulfinamidines under mild, metal-free conditions, achieving outstanding yields of up to 99%. Furthermore, we propose possible pathways that elucidate the observed molecular sequence of events in this reaction. This cutting-edge approach not only advances the synthesis of valuable sulfinamidine compounds but also expands the synthetic toolbox available to chemists, paving the way for future discoveries in organic synthesis and potential applications in medicinal chemistry.

Asymmetric Synthesis of S(IV) and S(VI) Stereogenic Centers

Sulfur can form diverse S(IV) and S(VI) stereogenic centers, of which some have gained significant attention recently due to their increasing use as pharmacophores in drug discovery programs. The preparation of these sulfur stereogenic centers in their enantiopure form has been challenging, and progress made will be discussed in this Perspective. This Perspective summarizes different strategies, with selected works, for asymmetric synthesis of these moieties, including diastereoselective transformations using chiral auxiliaries, enantiospecific transformations of enantiopure sulfur compounds, and catalytic enantioselective synthesis. We will discuss the advantages and limitations of these strategies and will provide our views on how this field will develop.

Hypervalent Iodine-Mediated Synthesis of Sulfinimidate Esters from Sulfenamides

In this study, we present a novel and efficient approach for the oxidative esterification of sulfenamides using phenyliodonium diacetate, enabling the synthesis of sulfinimidate esters and sulfilimines under mild and metal-free conditions, with yields reaching up to 99%. The protocol is readily scalable and compatible with a diverse range of substrates and functional groups, and we demonstrate its potential for late-stage functionalization of pharmacologically relevant molecules. Furthermore, we propose a plausible reaction mechanism to account for the observed sequence of events.

One-Pot Tandem Oxidative Bromination and Amination of Sulfenamide for the Synthesis of Sulfinamidines

The sulfinamidines as aza analogues of sulfinamides received limited attention from both organic chemists and pharmaceutical chemists. Herein, we present a tandem oxidative/nucleophilic substitution approach for the synthesis of sulfinamidines in high yield (up to 98%). This cascade reaction method is enabled by N-bromosuccinimide (NBS) as an oxidant and diverse readily available amines as nucleophiles without any additives or catalysts. Notably, this method is highly time-economical, safe to operate, and easy to scale up and has excellent functional group compatibility.

Dehydrogenative Imination of Low-Valent Sulfur Compounds-Fast and Scalable Synthesis of Sulfilimines, Sulfinamidines, and Sulfinimidate Esters

Herein, we describe an electrochemical pathway for the synthesis of sulfilimines, sulfoximines, sulfinamidines, and sulfinimidate esters from readily available low-valent sulfur compounds and primary amides or their analogues. The combination of solvents and supporting electrolytes together act both as an electrolyte as well as a mediator, leading to efficient use of reactants. Both can be easily recovered, enabling an atom-efficient and sustainable process. A broad scope of sulfilimines, sulfinamidines, and sulfinimidate esters with N-EWGs is accessed in up to excellent yields with broad functional group tolerance. This fast synthesis can be easily scaled up to multigram quantities with high robustness for fluctuation of current densities of up to 3 orders of magnitude. The sulfilimines are converted into the corresponding sulfoximines in an ex-cell process in high to excellent yields using electro-generated peroxodicarbonate as a green oxidizer. Thereby, preparatively valuable NH sulfoximines are accessible.

Unlocking geminal fluorohaloalkanes in nucleophilic fluoroalkylation chemistry: generation and trapping of lithiumfluorocarbenoids enabled by flow microreactors

A direct nucleophilic monofluoroalkylation strategy leveraging on lithium fluorocarbenoids has been developed. Flow microreactor technology allows capitalization of the synthetic potential of these scarcely explored short-lived intermediates - namely 1-fluoro-2-phenylethyllithium, 1-fluoro-3-phenylpropyllithium, and 1-fluorononyllithium - generated through lithium/iodine exchange reaction. This robust protocol was employed to prepare new fluorinated products, adopting various classes of electrophiles. The inherent advantages of microreactor technology contribute to rendering this approach a new valuable tool for direct fluoroalkylation chemistry.

(1R,2S,5R)-2-Isopropyl-5-methylcyclohexyl (R)-4-methylbenzenesulfonimidate

(1R,2S,5R)-2-isopropyl-5-methylcyclohexyl (R)-4-methylbenzenesulfonimidate was synthesized via the stereoselective NH-transfer to (1R,2S,5R)-2-isopropyl-5-methylcyclohexyl (S)-4-methylbenzenesulfinate. The reaction employed diacetoxyiodobenzene (DIB) and ammonium carbamate, and occurred in acetonitrile at room temperature. The imidation of sulfur proceeded with complete stereocontrol, and the reaction afforded the desired product as a single diastereoisomer and with high enantiocontrol (e.r. = 97:3) in 70% yield. The product was characterized by 1H-NMR, 13C-NMR, COSY, HSQC, IR spectroscopy, HRMS, and the enantiomeric ratio was established by HPLC analysis at the chiral stationary phase.

Synthesis of Sulfoximine Propargyl Carbamates under Improved Conditions for Rhodium Catalyzed Carbamate Transfer to Sulfoxides

Sulfoximines provide aza-analogues of sulfones, with potentially improved properties for medicinal chemistry. The sulfoximine nitrogen also provides an additional vector for the inclusion of other functionality. Here, we report improved conditions for rhodium catalyzed synthesis of sulfoximine (and sulfilimine) carbamates, especially for previously low-yielding carbamates containing π-functionality. Notably we report the preparation of propargyl sulfoximine carbamates to provide an alkyne as a potential click handle. Using Rh₂(esp)₂ as catalyst and a DOE optimization approach provided considerably increased yields.

Multistep Continuous Flow Synthesis of Isolable NH2 -Sulfinamidines via Nucleophilic Addition to Transient Sulfurdiimide

The growing interest in novel sulfur pharmacophores led to recent advances in the synthesis of some S(IV) and S(VI) motifs. However, preparation and isolation of uncommon primary sulfinamidines, the aza-analogues of sulfinamides, is highly desirable. Here we report a multistep continuous flow synthesis of poorly explored NH₂ -sulfinamidines by nucleophilic attack of organometallic reagents to in situ prepared N-(trimethylsilyl)-N-trityl-λ⁴ -sulfanediimine (Tr-N=S=N-TMS). The transformation can additionally be realized under mild conditions, at room temperature, via a highly chemoselective halogen-lithium exchange of aryl bromides and iodides with n-butyllithium. Moreover, the synthetic potential of the methodology was assessed by exploring further manipulations of the products and accessing novel S(IV) analogues of celecoxib, tasisulam, and relevant sulfinimidoylureas.

Practical Asymmetric Synthesis of Chiral Sulfoximines via Sulfur-Selective Alkylation

Chiral sulfoximines have recently been considered as promising bioisosteres in medicinal chemistry. However, methods for preparing chiral sulfoximines in a stereoselective manner are underdeveloped. Herein, we demonstrate an asymmetric synthesis of chiral sulfoximines through a stereospecific S-alkylation of readily accessible chiral sulfinamides under practical conditions. A key to establishing the practical conditions was the identification of the intermediate structure in our previously reported S-alkylation by X-ray crystallographic analysis.

Exploiting Configurational Lability in Aza-Sulfur Compounds for the Organocatalytic Enantioselective Synthesis of Sulfonimidamides

Methods for establishing the absolute configuration of sulfur‐stereogenic aza‐sulfur derivatives are scarce, often relying on cumbersome protocols and a limited pool of enantioenriched starting materials. We have addressed this by exploiting, for the first time, a feature of sulfonimidamides in which it is possible for tautomeric structures to also be enantiomeric. Such sulfonimidamides can readily generate prochiral ions, which we have exploited in an enantioselective alkylation process. Selectivity is achieved using a readily prepared bis‐quaternized phase‐transfer catalyst. The overall process establishes the capability of configurationally labile aza‐sulfur species to be used in asymmetric catalysis.

Direct synthesis of sulfenamides, sulfinamides, and sulfonamides from thiols and amines

Needless to say that organosulfur compounds with sulfur–nitrogen bonds have found various applications in diverse fields such as pharmaceuticals, agrochemicals, polymers, and so forth. Three major groups of such compounds are sulfenamides, sulfinamides, and sulfonamides which have been widely applied as building blocks in medical chemistry. Owing to their significant role in drug design and discovery programs, the search for and development of efficient, environmentally friendly, and economic processes for the preparation of the title compounds is of great importance in the pharmaceutical industry. Recently, oxidative coupling of thiols and amines, two readily available low-cost commodity chemicals, has emerged as a highly useful method for synthesizing structurally diverse sulfenamides, sulfinamides, and sulfonamides in a single step. Since this strategy does not require additional pre-functionalization and de-functionalization steps, it considerably streamlines synthetic routes and substantially reduces waste generation. This review will focus on recent advances and achievements in this attractive research arena.

This review provides a concise overview of the synthesis of biologically and synthetically valuable sulfenamide, sulfinamide, and sulfonamide derivatives through the direct oxidative coupling of readily available low-cost thiols and amines.

Sulfinimidate Esters as an Electrophilic Sulfinimidoyl Motif Source: Synthesis of N-Protected Sulfilimines from Grignard Reagents

In this work we investigated, for the first time, the reactivity of sulfinimidate esters as an electrophilic sulfinimidoyl motif source. The reaction of such sulfinimidate esters with Grignard reagents enables the preparation of protected sulfilimines in high yields and with a remarkable structural variability. Moreover, the transformation can be performed in CPME (cyclopentyl methyl ether) as a green solvent under environmentally responsible conditions.