Sulfinate Esters Research Articles

Recent Advances in the Electrochemical Synthesis of Organosulfur Compounds.

Organosulfur compounds are being widely used in medicinal chemistry, as well as in organic transformations and in synthetic applications. Because of their interest in many areas, the development of sustainable and green synthetic methods to access various organosulfur compounds has a high influence on the chemistry community. Electroorganic synthesis has become a very valuable methodology for the synthesis of organosulfur compounds during the last decade. The use of electrochemical technology offers a green, sustainable and safe alternative to prepare and modify such compounds. This review summarises recent developments in the preparation of organosulfur compounds such as sulfoxides, sulfones, sulfinic esters, sulfonamides, thiosulfonates, sulfonyl fluorides and sulfoximines under electrochemical reaction conditions.

Palladium-Catalyzed Sulfinylation of Aryl- and Alkenylborons with Sulfinate Esters

An efficient, direct sulfinylation of organoborons catalyzed by palladium is disclosed. Treatment of organoborons and sulfinate esters in the presence of a palladium precatalyst provided a broad range of sulfoxides. Various organosulfur compounds having oxidizable functional groups were successfully prepared through the sulfoxide synthesis.

NaHSO3‐Mediated Direct Synthesis of Sulfinic Esters from Sulfonyl Hydrazides under Transition‐Metal‐Free Conditions

AbstractWe have developed a protocol for the NaHSO3‐promoted esterification of sulfonyl hydrazides with alcohols for the synthesis of sulfinic esters. Various sulfonyl hydrazides could be converted to the corresponding sulfinic esters in good to high yields. The merits of this protocol include mild transition‐metal‐free reaction conditions, an inexpensive and available reagent, and operational simplicity. Controlled experiments reveal that this transformation probably undergoes via a radical pathway.magnified image

Electrochemical Oxidative Esterification of Thiophenols: Efficient Access to Sulfinic Esters.

The sulfinic esters are important and useful building blocks in organic synthesis. The aim of this study was to develop a simple and efficient method for the synthesis of sulfinic esters. Constant current electrolysis from thiols and alcohols was selected as the method for the synthesis of sulfinic esters. A novel electrochemical method for the synthesis of sulfinic esters from thiophenols and alcohols has been developed. Up to 27 examples of sulfinic esters have been synthesized using the current methods. This protocol shows good functional group tolerance as well as high efficiency. In addition, this protocol can be easily scaled up with good efficiency. Notably, heterocycle-containing substrates, including pyridine, thiophene, and benzothiazole, gave the desired products in good yields. A plausible reaction mechanism is proposed. This research not only provides a green and efficient method for the synthesis of sulfinic esters but also shows new applications of electrochemistry in organic synthesis. It is considered that this green and efficient synthetic protocol used to prepare sulfinic esters will have good applications in the future.

Silver/Palladium Relay Catalyzed Cross‐Coupling of N'‐Acetyl‐8‐quinolinesulfonylhydrazide with Alcohols: An Easy Access to 8‐Quinolinesulfinate Esters

An efficient strategy for the synthesis of unexplored 8‐quinolinesulfinate esters has been reported. The method involves in situ generation of quinoline sulfinate from N'‐acetylquinoline‐8‐sulfonohydrazide via silver mediated cleavage followed by palladium‐catalyzed cross‐coupling with 1° and 2° alcohols to yield sulfinate esters. A variety of substituted alcohols were successfully employed in the reaction. Control experiments performed to understand the mechanism, revealed that the transformation follows a radical pathway and the alcohol oxygen get incorporated in the resulting sulfinate esters. Two of the chirally pure alcohols were also used in the transformation to study the diastereoselectivity in the reaction. In order to demonstrate the synthetic utility, a representative allyl‐quinoline‐8‐sulfinate 3f was successfully converted into the 8‐(allylsulfonyl)‐quinoline 4 via palladium(II) acetate mediated isomerization.

Electrochemical Synthesis of Sulfinate Esters: Nickel(II)-Catalyzed Oxidative Esterification of Thiols with Alcohols in an Undivided Cell.

In this study, nickel-catalyzed electrochemical oxidative esterification of thiols with alcohols for the synthesis of sulfinate esters has been reported. The electrochemical oxidative esterification proceeded through a nickel-catalyzed oxidation of thiols using an undivided cell of graphite/nickel electrodes, where the nickel oxidation was studied by cyclic voltammetry. The method was conveniently and directly used for the one-pot synthesis of sulfinate esters of thiols.

One-pot Synthesis of Allyl Sulfides from Sulfinate Esters and Allylsilanes through Reduction of Alkoxysulfonium Intermediates

An efficient method to synthesize allyl sulfides from sulfinate esters and allylsilanes is described. Based on the reactivity of isolated allyl(methoxy)phenyl sulfonium triflate, we have developed a simple one-pot method for the allyl sulfide synthesis by S-allylation of sulfinate esters and subsequent reduction with sodium borohydride. A number of allyl sulfides were prepared by this method leaving various functional groups unreacted.

Synthesis and Antibacterial Screening of Some Pyrazole Derivatives Catalyzed by Cetyltrimethylammoniumbromide (CTAB).

In this article, we have developed an eco-friendly one-pot multi-component reaction methodology employed for the green synthesis of functionalized pyrazole derivatives viz cyclo-condensation of aromatic aldehydes, ethyl acetoacetate and phenyl hydrazine and/or hydrazine hydrate in the presence of cetyltrimethylammoniumbromide (CTAB) at 90°C temperature in an aqueous medium. In the present protocol, we developed a green method for the synthesis of functionalized pyrazole derivatives through one-pot, multi-component cyclo-condensation of aromatic aldehydes, phenyl hydrazine or hydrazine hydrate and ethyl acetoacetate using cetyltrimethylammoniumbromide (CTAB) as a catalyst in water as a solvent. Our methodology confers advantages such as short reaction time, atom economy, purification of the product without using column chromatographic and hazardous solvent. The reaction is being catalyzed by cetyltrimethylammoniumbromide (CTAB) and thus, products are formed under the green reaction conditions. Initially, the reaction of benzaldehyde and phenylhydrazine with ethyl acetoacetate was carried out in water at room temperature in the absence of the catalyst; no product was obtained after 24 h (Table 1 entry 1). When the reaction was carried out using L-proline as a catalyst in ethanol at 70°C, the yield of the product was 20%. This research not only provides a green and efficient method for the synthesis of sulfinic esters but also shows new applications of electrochemistry in organic synthesis. We consider that this green and efficient synthetic protocol used to prepare sulfinic esters will have good applications in the future. In conclusion, we have developed successfully a green and efficient one-pot multi-component methodology for the synthesis of substituted pyrazoles using CTAB as a catalyst in water as a solvent with excellent yields. Purifications of compounds were achieved without the use of traditional chromatographic procedures. This methodology has advantages of operational simplicity, clean reaction profiles and relatively broad scope, which make it more attractive for the diversity oriented synthesis of these heterocyclic libraries. In this methodology, we suggest a further alternative possibility for the formation of substituted pyrazoles. The compound 7h can be used as an anticancer drug in the pharma industry.

Electrochemical Synthesis of Sulfinic Esters via Aerobic Oxidative Esterification of Thiophenols with Alcohols

A method for the electrochemical synthesis of sulfinic esters by aerobic oxidative coupling of thiophenols and alcohols has been developed. Using electrons as the redox reagent and O2 in air as the oxygen source, the reactions proceeded smoothly at room temperature, even for a gram-scale preparation. No use of catalyst, clean redox reagent, green and abundant oxygen source, and mild reaction conditions make this strategy eco-friendly.

Post-functionalization of dibenzothiophene to functionalized biphenyls via a photoinduced thia-Baeyer-Villiger oxidation

The Baeyer-Villiger reaction is used extensively in organic chemistry. Sila- and bora-variants have also been documented widely, with these processes underpinning, for example, the Fleming-Tamao oxidation and hydroborative alkene hydration, respectively. By contrast, the development of thia-Baeyer-Villiger reactions involving sulfoxides has long been considered unlikely because competitive oxidation to the sulfone occurs exclusively. Here, we disclose a photoinduced thia-Baeyer-Villiger-type oxidations; specifically, we find that exposure of dibenzothiophene (DBT) derivatives to an iron porphyrin catalyst under Ultraviolet irradiation in the presence of t-BuOOH generates sulfinic esters in up to 87% yield. The produced sulfinic esters are transformed to a variety of biphenyl substrates including biphenyl sulfoxides, sulfones and sulfonamides in 1-2 steps. These results provide a mild process for the selective functionalization of sulfur compounds, and offer a biomimetic approach to convert DBT into 2-hydroxybiphenyl under controllable stepwise pathway. Based upon experimental evidences and DFT calculation, a mechanism is proposed.

Electrochemical synthesis of sulfinic esters from alcohols and thiophenols

Electrochemical oxidative couplings between SH and OH bonds are achieved herein directly from readily-available alcohols and thiophenols, affording a series of diverse sulfinic esters. This strategy can take advantage of 6 equivalents of alcohol, relative to thiophenol, to achieve moderate to good yields, without the assistance of any metallic catalysts, bases, and additional oxidants.

Sulfoxide synthesis from sulfinate esters under Pummerer-like conditions.

A facile synthetic method for the preparation of allyl sulfoxides by S-allylation of sulfinate esters proceeds through sulfonium intermediates without [3,3]-sigmatropic rearrangement and further Pummerer-type reactions of the resulting allyl sulfoxides. On the basis of the plausible reaction mechanism involving sulfonium salt intermediates, S-alkynylation and S-arylation were also accomplished.

Efficient electrosynthesis of sulfinic esters via oxidative cross‐coupling between alcohols and thiophenols

AbstractA new protocol for SO bond formation was developed by electrochemical oxidative cross‐coupling between alcohols and thiophenols. With this strategy, a series of valuable sulfinic ester derivatives were synthesized up to 96% yield from basic starting materials. A preliminary mechanistic investigation reveals that this reaction involves oxygen reduction reaction (ORR).

Facial synthesis of sulfinic esters via copper-catalyzed reaction of sulfonyl hydrazides with alcohols in air

The efficient Cu-catalyzed esterification of sulfonyl hydrazides with alcohols in air is described, providing sulfinic esters in good yields and broad scope. Mechanistic studies suggest that the reaction likely proceeds through free-radical formation including arylthio radical and arylsulfonyl radical, while arylsulfuric acid are the major esterification intermediate in this transformation.

Rh-catalyzed intramolecular cyclization of 1-sulfonyl-1,2,3-triazole and sulfinate. Concise preparation of sulfonylated unsaturated piperidines

When 4-[3-(methanesulfinyloxy)propyl]-1-(arenesulfonyl)-1,2,3-triazoles were treated with rhodium catalysts of the type Rh2(RCO2)4, a new intramolecular cyclization took place to afford 2,3-didehydro-1-(arenesulfonyl)-3-(methanesulfonyl)piperidines in good yields. This reaction most likely proceeds via a new reorganization of bonds in the same molecule, consisting of the addition of the sulfur atom of sulfinate ester to the α-(sulfonylimino)carbene moiety generated from the sulfonyltriazole, followed by the counter attack of the sulfonylimino nitrogen to the carbon bearing the oxygen terminus of sulfinate ester.

Metal- and oxidant-free electrochemical synthesis of sulfinic esters from thiols and alcohols

An eco-friendly electrochemical synthesis of sulfinic esters from thiols and alcohols under mild reaction conditions has been developed.

Efficient Synthesis of Sulfinate Esters and Sulfinamides via Activated­ Esters of p-Toluenesulfinic Acid

Sulfinate esters were prepared by the process of activating p-toluenesulfinic acid with either cyanuric chloride, methanesulfonyl chloride, or 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC-HCl). Activation of p-toluenesulfinic acid with cyanuric chloride led to the formation of sulfinate esters that were accompanied by the formation of the corresponding sulfones. The use of methanesulfonyl chloride for activation via methanesulfonic p-toluenesulfinic anhydride afforded mixtures of sulfinate esters and methanesulfonates. The use of the carbodiimide EDC proved to yield the best results with the highly selective formation of the target sulfinate esters. The use of trimethylacetic p-toluenesulfinic anhydride or cyanuric chloride to achieve the synthesis of sulfinamides proved to be ineffective due to poor chemoselectivity of the nucleophilic attack on the activated p-toluenesulfinic acid anhydride. Ultimately, the use of EDC-HCl to form the sulfinamides proved to be the best pathway for synthesis.

Highly Chemoselective NH- and O-Transfer to Thiols Using Hypervalent Iodine Reagents: Synthesis of Sulfonimidates and Sulfonamides.

Aryl thiols can be selectively converted to sulfonimidates or sulfonamides with three new S-X connections being made selectively in one pot. Using hypervalent iodine reagents in the presence of ammonium carbamate, NH- and O-groups are transferred under mild and practical conditions. Reducing the loading of ammonium carbamate changed the product distribution, converting the sulfonimidate to the sulfonamide. Studies into the possible intermediate species are presented, suggesting that multiple pathways may be possible via sulfinate esters, or related intermediates, with each species forming the same products.

Highly Sensitive Bioluminescent Probe for Thiol Detection in Living Cells.

The sensitive detection of thiols including glutathione and cysteine is desirable owing to their roles as indispensable biomolecules in maintaining intracellular biological redox homeostasis. Herein, we report the design and synthesis of SEluc-1 (sulfinate ester luciferin), a chemoselective probe exhibiting a ratiometric and turn-on response towards thiols selectively in fluorescence and bioluminescence, respectively. The probe, which was designed based on the "caged" luciferin strategy, displays excellent selectivity, high signal/noise ratio (>240 in the case of bioluminescence), and a biologically relevant limit of detection (LOD, 80 nm for cysteine), which are all desirable traits for a sensitive bioluminescent sensor. SEluc-1 was further applied to fluorescence imaging of thiol activity in living human cervical cancer HeLa cell cultures, and was successfully able to detect fluctuations in thiol concentrations induced by oxidative stress in a bioluminescent assay utilizing African green monkey fibroblast COS-7 cells and human breast adenocarcinoma MCF-7 cells.

Copper-Catalyzed Oxidative Reaction of β-Keto Sulfones with Alcohols via C-S Bond Cleavage: Reaction Development and Mechanism Study.

A Cu-catalyzed cascade oxidative radical process of β-keto sulfones with alcohols has been achieved by using oxygen as an oxidant. In this reaction, β-keto sulfones were converted into sulfinate esters under the oxidative conditions via cleavage of C-S bond. Experimental and computational studies demonstrate that a new pathway is involved in this reaction, which proceeds through the formation of the key four-coordinated CuII intermediate, O-O bond homolysis induced C-S bond cleavage and Cu-catalyzed esterification to form the final products. This reaction provides a new strategy to sulfonate esters and enriches the research content of C-S bond cleavage and transformations.