Synthesis of Pyrazolesulfoximines Using α-Diazosulfoximines with Alkynes

Sulfoximines and pyrazoles are both important motifs in medicinal compounds. Here we report the synthesis and reactivity of sulfoximine diazo compounds as new reagents for the incorporation of sulfoximines. The use of N-silyl sulfoximines enabled formation of monosubstituted diazo compounds. Their application is demonstrated in a [3 + 2] cycloaddition with alkynes to form pyrazole sulfoximines in a new combination of these important chemotypes. Further derivatization of the pyrazole sulfoximines is demonstrated, including silyl deprotection to form unprotected pyrazolesulfoximines.

I2-Mediated [6 + 1] Annulation of Alkynes with MsONH3OTf: Direct Synthesis of Benzo[b]azepines

The synthesis of benzo[b]azepines using protonated aminating reagent (MsONH₃OTf) and alkynes through I₂-mediated [6 + 1] annulation reaction has been developed. This protocol features excellent functional group tolerance and mild reaction conditions and affords the benzo[b]azepines in moderate to good yields under metal-free reaction conditions.

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.

The advent of electrophilic hydroxylamine-derived reagents for the direct preparation of unprotected amines

Electrophilic aminating reagents have seen a renaissance in recent years as effective nitrogen sources for the synthesis of unprotected amino functionalities. Based on their reactivity, several noble and non-noble transition metal catalysed amination reactions have been developed. These include the aziridination and difunctionalisation of alkenes, the amination of arenes as well as the synthesis of aminated sulfur compounds. In particular, the use of hydroxylamine-derived (N-O) reagents, such as PONT (PivONH3OTf), has enabled the introduction of unprotected amino groups on various different feedstock compounds, such as alkenes, arenes and thiols. This strategy obviates undesired protecting-group manipulations and thus improves step efficiency and atom economy. Overall, this feature article gives a recent update on several reactions that have been unlocked by employing versatile hydroxylamine-derived aminating reagents, which facilitate the generation of unprotected primary, secondary and tertiary amino groups.

Iron‐Catalyzed Intramolecular Arene C(sp 2 )−H Amidations under Mechanochemical Conditions

In a ball mill, FeBr₃‐catalyzed intramolecular amidations lead to 3,4‐dihydro‐2(1H)‐quinolinones in good to almost quantitative yields. The reactions do not require a solvent and are easy to perform. No additional ligand is needed for the iron catalyst. Both 4‐substituted aryl and β‐substituted dioxazolones provide products with high selectivity. Mechanistically, an electrophilic spirocyclization followed by C−C migration explains the formation of rearranged products.

A Combined Spectroscopic and Computational Study on the Mechanism of Iron-Catalyzed Aminofunctionalization of Olefins Using Hydroxylamine Derived N-O Reagent as the "Amino" Source and "Oxidant"

Herein, we study the mechanism of iron-catalyzed direct synthesis of unprotected aminoethers from olefins by a hydroxyl amine derived reagent using a wide range of analytical and spectroscopic techniques (Mössbauer, Electron Paramagnetic Resonance, Ultra-Violet Visible Spectroscopy, X-ray Absorption, Nuclear Resonance Vibrational Spectroscopy, and resonance Raman) along with high-level quantum chemical calculations. The hydroxyl amine derived triflic acid salt acts as the “oxidant” as well as “amino” group donor. It activates the high-spin Fe(II) (S_t = 2) catalyst [Fe(acac)₂(H₂O)₂] (1) to generate a high-spin (S_t = 5/2) intermediate (Int I), which decays to a second intermediate (Int II) with S_t = 2. The analysis of spectroscopic and computational data leads to the formulation of Int I as [Fe(III)(acac)₂-N-acyloxy] (an alkyl-peroxo-Fe(III) analogue). Furthermore, Int II is formed by N–O bond homolysis. However, it does not generate a high-valent Fe(IV)(NH) species (a Fe(IV)(O) analogue), but instead a high-spin Fe(III) center which is strongly antiferromagnetically coupled (J = −524 cm^–1) to an iminyl radical, [Fe(III)(acac)₂-NH·], giving S_t = 2. Though Fe(NH) complexes as isoelectronic surrogates to Fe(O) functionalities are known, detection of a high-spin Fe(III)-N-acyloxy intermediate (Int I), which undergoes N–O bond cleavage to generate the active iron–nitrogen intermediate (Int II), is unprecedented. Relative to Fe(IV)(O) centers, Int II features a weak elongated Fe–N bond which, together with the unpaired electron density along the Fe–N bond vector, helps to rationalize its propensity for N-transfer reactions onto styrenyl olefins, resulting in the overall formation of aminoethers. This study thus demonstrates the potential of utilizing the iron-coordinated nitrogen-centered radicals as powerful reactive intermediates in catalysis.

Hydroxylamine-Derived Reagent as a Dual Oxidant and Amino Group Donor for the Iron-Catalyzed Preparation of Unprotected Sulfinamides from Thiols

An iron catalyzed reaction for the selective transformation of thiols (-SH) to sulfinamides (-SONH2 ) by a direct transfer of -O and free -NH2 groups has been developed. The reaction operates under mild conditions using a bench stable hydroxylamine derived reagent, exhibits broad functional group tolerance, is scalable and proceeds without the use of any precious metal catalyst or additional oxidant. This novel, practical reaction leads to the formation of two distinct new bonds (S=O and S-N) in a single step to chemoselectively form valuable, unprotected sulfinamide products. Preliminary mechanistic studies implicate the role of the alcoholic solvent as an oxygen atom donor.

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

In this work we report a new synthetic tactic for the straightforward preparation of hardly accessible sulfinamidines and sulfinamide esters, by using a simple metal-free protocol. The process is robust and uses readily available sulfenamides as the S-donor and sulfonyloxycarbamates as the N-source. The scope and mechanism have also been investigated.

Synthesis of NH-Sulfoximines by Using Recyclable Hypervalent Iodine(III) Reagents under Aqueous Micellar Conditions

The synthesis of NH-sulfoximines from sulfides has been first developed under mild conditions in an aqueous solution with surfactant TPGS-750-M as the catalyst at room temperature. In this newly developed process, a simple and convenient recycling strategy to regenerate the indispensable hypervalent iodine(III) is used. The resulting 1,2,3-trifluoro-5-iodobezene can be recovered almost quantitively from the mixture by liquid-liquid extraction and then oxidized to give the corresponding iodine(III) species. This optimized procedure is compatible with a broad range of functional groups and can be easily performed on a gram scale, providing a green protocol for the synthesis of sulfoximines.

Batch and Continuous-Flow Iron(II)-Catalyzed Synthesis of Sulfilimines and Sulfoximines using N-Mesyloxycarbamates

The synthesis of sulfilimines and sulfoximines with N-mesyloxycarbamates in presence of catalytic iron(II) chloride hydrate is described. The use of 1-butylimidazole as a base proved instrumental in enabling a homogeneous reaction mixture compatible with continuous flow processes. The amination is applicable to a wide range of substrates, and affords the desired product in good to excellent yields within 1 to 60 minutes.

SuFEx Chemistry of Thionyl Tetrafluoride (SOF4 ) with Organolithium Nucleophiles: Synthesis of Sulfonimidoyl Fluorides, Sulfoximines, Sulfonimidamides, and Sulfonimidates

Thionyl tetrafluoride (SOF4 ) is a valuable connective gas for sulfur fluoride exchange (SuFEx) click chemistry that enables multidimensional linkages to be created via sulfur-oxygen and sulfur-nitrogen bonds. Herein, we expand the available SuFEx chemistry of SOF4 to include organolithium nucleophiles, and demonstrate, for the first time, the controlled projection of sulfur-carbon links at the sulfur center of SOF4 -derived iminosulfur oxydifluorides (R1 -N=SOF2 ). This method provides rapid and modular access to sulfonimidoyl fluorides (R1 -N=SOFR2 ), another array of versatile SuFEx connectors with readily tunable reactivity of the S-F handle. Divergent connections derived from these valuable sulfonimidoyl fluoride units are also demonstrated, including the synthesis of sulfoximines, sulfonimidamides, and sulfonimidates.

O-Substituted hydroxyl amine reagents: an overview of recent synthetic advances

Reagents derived from oxygen-substituted hydroxylamine facilitate stereo- and regioselective C–N, N–N, O–N, and S–N bond-formation reactions and intra-molecular cyclizations without any expensive metal catalysts. These remarkable transformations are discussed in this review.