PhI(OAc)2/KI mediated 1,2-acetoxysulfenylation of alkenes: facile synthesis of β-acetoxysulfides

Straightforward Functionalization of Sulfur-Containing Peptides via 5- and 6-endo-dig Cyclization Reactions

We present a simple and convenient method for the generation of sulfenyl electrophiles from peptides containing S–S or S–H bonds by employing N-chlorosuccinimide. The corresponding sulfenyl electrophiles are further utilized in 5- and 6-endo-dig cyclization reactions yielding indolizinium salts, indoles, benzo[b]furans, polyaromatic hydrocarbons (PAHs) and isocoumarins, as well as quinolinones bearing a glutathione moiety. PAH derivatives can be used as selective fluorescent dyes for the visualization of lipid droplets in living cells.

Experimental and DFT Studies on the Identity Exchange Reactions between Phenyl Chalcogen Iranium Ions and Alkenes

The gas-phase ion-molecule identity exchange reactions of phenyl chalcogen iranium ions with alkenes have been examined experimentally in a linear ion trap mass spectrometer by isotope labeling experiments. The nature of both the alkene and the chalcogen play crucial roles, with the bimolecular rates for π-ligand exchange following the order: [PhTe(c-C₆H₁₀)]⁺ + c-C₆D₁₀ > [PhTe(C₂D₄)]⁺ + C₂H₄ > [PhSe(c-C₆H₁₀)]⁺ + c-C₆D₁₀, with no reaction being observed for [PhSe(C₂D₄)]⁺ + C₂H₄, [PhS(C₂D₄)]⁺ + C₂H₄, and [PhS(c-C₆H₁₀)]⁺ + c-C₆D₁₀. The experimental results correlate with RRKM modeling and density functional theory (DFT) calculations, which also demonstrates that these reactions proceed via associative mechanisms. Natural bond orbital (NBO) analysis reveals a shift in the association complexes from a σ-hole interaction to ones mirroring the π-p⁺ and n-π* at the transition state in accordance with the rates of reaction.

Reactions of Thiiranium and Sulfonium Ions with Alkenes in the Gas Phase

Ion-molecule reactions between thiiranium ion 11 (m/z 213) and cyclohexene and cis-cyclooctene resulted in the formation of addition products 17a and 17b (m/z 295 and m/z 323, respectively) via an electrophilic addition pathway. Associative π-ligand exchange involving direct transfer of the PhS⁺ moiety, which has been observed for analogous seleniranium ions in the gas phase, did not occur despite previous solution experiments suggesting it as a valid pathway. DFT calculations at the M06-2X/def2-TZVP level of theory showed high barriers for the exchange reaction, while the addition pathway was more plausible. Further support for this pathway was provided with Hammett plots showing the rate of reaction to increase as the benzylic position of thiiranium ion derivatives became more electrophilic (ρ = +1.69; R² = 0.974). The more reactive isomeric sulfonium ion 22 was discounted as being responsible for the observed reactivity with infrared spectroscopy and DFT calculations suggesting little possibility for isomerization. To further explore the differences in reactivity, thiiranium ion 25 and sulfonium ion 27 were formed independently, with the latter ion reacting over 260 times faster toward cis-cyclooctene than the thiiranium ion rationalized by calculations suggesting a barrierless pathway for sulfonium ion 27 to react with the cycloalkene.

β-Hydroxy sulfides and their syntheses

Sulfur-containing natural products are ubiquitous in nature, their most abundant source being marine organisms since sulfur, in the form of the sulfate ion, is the second most abundant anion in sea water after chloride. As part of natural products, sulfur can appear in a multitude of combinations and oxidation states: thiol, sulfide (acyclic or heterocyclic), disulfide, sulfoxide, sulfonate, thioaminal, hemithioacetal, various thioesters, thiocarbamate and isothiocyanate. This review article focuses on β-hydroxy sulfides and analogs; their presence in natural products, general protocols for their synthesis, and examples of their application in target oriented synthesis.

Three-component difunctionalization of alkenes leading to β-acetamido sulfides and β-acetoxy sulfides

A novel method for the synthesis of β-acetamido sulfides via NBS-mediated aminosulfenylation of alkenes with thiophenols and nitriles under metal-free conditions has been described. And β-acetamido sulfides were also synthesized with 1-(arylthio)pyrrolidine-2,5-diones as substrates and HBr as an additive. On the other hand, iodine-catalyzed 1,2-acetoxysulfenylation of alkenes by using (diacetoxyiodo)benzene as an oxygen source to synthesise various β-acetoxy sulfides was described as well.

Iodine-mediated synthesis of 4-selanylpyrazoles

A new and simple procedure mediated by I₂ is developed for the preparation of 4-selanylpyrazoles from pyrazoles and diselenides.

Synthesis of N-alkyl-3-sulfonylindoles and N-alkyl-3-sulfanylindoles by cascade annulation of 2-alkynyl-N,N-dialkylanilines

Divergent synthesis of N-alkyl-3-sulfonylindoles and N-alkyl-3-sulfanylindoles from 2-alkynyl-N,N-dialkylanilines and sulfonyl hydrazides has been described.

Convenient iodine-mediated aminoselenation of alkenes using benzotriazoles as nitrogen sources

Convenient iodine-mediated alkene aminoselenation using benzotriazoles as nitrogen sources.

Enantioselective Synthesis of β-Hydrazino Alcohols Using Alcohols and N-Boc-Hydrazine as Substrates

An enantioselective approach for the synthesis of α-hydrazino aldehydes is described that utilizes alcohols and N-Boc hydrazine instead of the conventional combination of aldehydes with azodicarboxylates. This protocol is enabled by merging in situ aerobic dual oxidation with asymmetric organocatalysis. This reaction also exhibits a high tolerance for varieties of substituents on the alcohol component. This approach features excellent enantiocontrol, cheap starting materials, operational simplicity, and scalability. The corresponding chiral β-hydrazino alcohols were obtained by sequential reduction with excellent enantioselectivity (up to 98% ee).

Three-component oxysulfenylation reaction: two simple and convenient approaches to β-alkoxy sulfides

An unprecedented method for the synthesis of β-alkoxy sulfides via a NaI/HBr-mediated three-component oxysulfenylation reaction of alkenes with arylsulfinic acids and alcohols is reported. Furthermore, I2-promoted oxysulfenylation of alkenes using sodium arylsulfinates instead of arylsulfinic acids to synthesise various β-alkoxy sulfides is also described.

Iodine-catalyzed Sulfonylation of Arylacetylenic Acids and Arylacetylenes with Sodium Sulfinates: Synthesis of Arylacetylenic Sulfones

A highly efficient and generally applicable iodine-catalyzed reaction of arylacetylenic acids and arylacetylenes with sodium sulfinates for the synthesis of arylacetylenic sulfones was developed. The methodology has the advantages of a metal-free strategy, easy to handle reagents, functional group tolerance, a wide range of arylacetylenic acids and arylacetylenes, and easy access to arylacetylenic sulfones.

Advances in Synthetic Applications of Hypervalent Iodine Compounds

The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C-C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of using hypervalent iodine compounds as an environmentally sustainable alternative to heavy metals.

PIDA–I2 mediated direct vicinal difunctionalization of olefins: iodoazidation, iodoetherification and iodoacyloxylation

I⁺ (IOAc) was produced from the combination of phenyliodine diacetate (PIDA) and iodine.

PIFA-mediated ethoxyiodination of enamides with potassium iodide

The combination of PIFA with KI in ethanol triggers the regioselective ethoxyiodination of a broad range of enamides with excellent yields and diastereoselectivities.

PhI(OAc)2 mediated decarboxylative sulfonylation of β-aryl-α,β-unsaturated carboxylic acids: a synthesis of (E)-vinyl sulfones

A highly efficient metal-free decarboxylative sulfonylation protocol for the preparation of (E)-vinyl sulfones from of β-aryl-α,β-unsaturated carboxylic acids using sodium sulfinates and (diacetoxyiodo)benzene (PhI(OAc)2) was developed. This strategy offers a simple and expedient synthesis of (E)-vinyl sulfones bearing a wide variety of functional groups. A radical-based pathway has been proposed for this decarboxylative sulfonylation reaction.

Metal-free oxysulfenylation of alkenes with 1-(arylthio)pyrrolidine-2,5-diones and alcohols

An easy and efficient metal-free approach to β-alkoxy sulfides has been developed. The protocol uses readily available 1-(arylthio)pyrrolidine-2,5-diones and alcohols as the oxysulfenylating agents, chloroform as the solvent, and no ligand, additive and exclusion of air were required.

Silver-catalyzed direct spirocyclization of alkynes with thiophenols: a simple and facile approach to 3-thioazaspiro[4,5]trienones

A convenient and efficient silver-catalyzed direct oxidative spirocyclization of alkynes with thiophenols leading to 3-thioazaspiro[4,5]trienones has been developed under air.