Reduction of Sulfur Dioxide to Sulfur Monoxide by Ferrous Porphyrin**

The reduction of SO₂ to fixed forms of sulfur can address the growing concerns regarding its detrimental effect on health and the environment as well as enable its valorization into valuable chemicals. The naturally occurring heme enzyme sulfite reductase (SiR) is known to reduce SO₂ to H₂S and is an integral part of the global sulfur cycle. However, its action has not yet been mimicked in artificial systems outside of the protein matrix even after several decades of structural elucidation of the enzyme. While the coordination of SO₂ to transition metals is documented, its reduction using molecular catalysts has remained elusive. Herein reduction of SO₂ by iron(II) tetraphenylporphyrin is demonstrated. A combination of spectroscopic data backed up by theoretical calculations indicate that Fe^IITPP reduces SO₂ by 2e⁻/2H⁺ to form an intermediate [Fe^III−SO]⁺ species, also proposed for SiR, which releases SO. The SO obtained from the chemical reduction of SO₂ could be evidenced in the form of a cheletropic adduct of butadiene resulting in an organic sulfoxide.     

Templated Total Synthesis of Cu(I)-Methanobactin OB3b**

Methanobactin OB3b (Mbn-OB3b) is a unique natural product with stunning affinity for copper ions (K_a≈Cu(I) 10³⁴). Here, we report the first total synthesis of Cu(I)-bound methanobactin OB3b featuring as key transformations a cyclodehydration-thioacylation sequence, to generate the conjugated heterocyclic systems, and a copper-templated cyclization, to complete the caged structure of the very sensitive target compound.     

含硫套索冠醚的合成

将二氮杂１８－冠－６的乙腈溶液分别与２－氯乙基烷基硫醚、２－氯乙基烯丙基硫醚、［２－（２－ｒ氯乙基）硫乙基］烷基硫醚在无水碳酸钾存在下反应制得５种新型侧链上含硫原子的双臂套索冠醚和５种新型单臂套索冠醚。它们的收率分别为３７％－７２％和１３％－３７％。此法比其它制备单臂套索冠醚的方法操作简单。     

Comprehensive Study of the Enhanced Reactivity of Turbo-Grignard Reagents**

Since its introduction in 2004, Knochel's so called Turbo-Grignard reagents revolutionized the usage of Grignard reagents. Through the simple addition of LiCl to a magnesium alkyl an outstanding increase in reactivity can be achieved. Though the exact composition of the reactive species remained mysterious, the reactive mixture itself is readily used not only in synthesis but also found its way into more distant fields like material science. To unravel this mystery, we combined single-crystal X-ray diffraction with in-solution NMR-spectroscopy and closed our investigations with quantum chemical calculations. Using such a variety of methods, we have gained insight into and an explanation for the extraordinary reactivity of this extremely convenient reagent by determining the structure of the first bimetallic reactive species [t-Bu₂Mg ⋅ LiCl ⋅ 4 thf] with two tert-butyl anions at the magnesium center and incorporated lithium chloride.     

Carbon-Carbon Bond Formation from Carbon Monoxide and Hydride: The Role of Metal Formyl Intermediates**

Current examples of carbon chain production from metal formyl intermediates with homogeneous metal complexes are described in this Minireview. Mechanistic aspects of these reactions as well as the challenges and opportunities in using this understanding to develop new reactions of CO and H₂ are also discussed.     

Rate Study for Electron Transfer of Sml2 to the Carbonyl Compounds and the Sulfoxides

The rate constants for the electron transfer of samarium diiodide to 2-heptanal, 2-methyl valeraldehyde and diphenyl sulfoxide were obtained for the first time. The reaction is first order in these substrates and there are hints that the reaction rate has a strong steric dependence. HMPA exhibited a profound catalytic effect but t-BuOH did not. The effect of temperature on reaction rates was also obtained.     

Synthesis and Fungicidal Activities of 4H-Imidazolin-4-ones Containing Sulfur Substituent

4H-Imidazolin-4-ones 3 and 4 were synthesized respectively by base catalytic reactions of 4-methylthiophenol or phenthiol with carbodiimides 2 , which were obtained via aza-Wittig reaction of iminophosphorane 1 with aromatic isocyanates. 3 and 4 exhibited good fungicidal activity against Pellicularia sasakii.     

Synthesis of Complex Thiazoline-Containing Peptides by Cyclodesulfhydration of N-Thioacyl-2-Mercaptoethylamine Derivatives

Herein we report a mild, efficient, and epimerization-free method for the synthesis of peptide-derived 2-thiazolines and 5,6-dihydro-4H-1,3-thiazines based on a cyclodesulfhydration of N-thioacyl-2-mercaptoethylamine or N-thioacyl-3-mercaptopropylamine derivatives. The described reaction can be easily carried out in aqueous solutions at room temperature and it is triggered by change of the pH, leading to complex thiazoline or dihydrothiazine derivatives without epimerization in excellent to quantitative yields. The new method was applied in the total synthesis of the marine metabolite mollamide F, resulting in the revision of its stereochemistry.     

X-Ray-triggered Carbon Monoxide and Manganese Dioxide Generation based on Scintillating Nanoparticles for Cascade Cancer Radiosensitization

Carbon monoxide (CO) is an endogenous signaling molecule with broad therapeutic effects. Here, a multifunctional X-ray-triggered carbon monoxide (CO) and manganese dioxide (MnO₂) generation nanoplatform based on metal carbonyl and scintillating nanoparticles (SCNPs) is reported. Attributed to the radioluminescent characteristic of SCNPs, UV-responsive Mn₂(CO)₁₀ is not only indirectly activated to release CO by X-ray but can also be degraded into MnO₂. A high dose of CO can be used as a glycolytic inhibitor for tumor suppression; it will also sensitize tumor cells to radiotherapy. Meanwhile MnO₂, as the photolytic byproduct of Mn₂(CO)₁₀, has both glutathione (GSH) depletion and Fenton-like Mn²⁺ delivery properties to produce highly toxic hydroxyl radical (⋅OH) in tumors. Thus, this strategy can realize X-ray-activated CO release, GSH depletion, and ⋅OH generation for cascade cancer radiosensitization. Furthermore, X-ray-activated Mn²⁺ in vivo demonstrates an MRI contrast effect, making it a potential theranostic nanoplatform.     

Synthesis and Studies of Some Nitrogen and Sulfur Compounds

Pyrazolo-, pyrimidino-, isoxazolo-, thiozolo-, and g -lactam incorporating thienopyridazine has been synthesised by cyclocondensation addition reaction and cycloaddition reaction of hydrazine hydrate phenyl hydrazine, hydroxylamine hydrochloride, urea, thiourea, mercapto acetic acid and monochloroacetyl chloride.     

Sulfoxides as ‘traceless’ resolving agents for the synthesis of atropisomers by dynamic or classical resolution

Reacting (−)-menthyl sulfinate with an atropisomeric but racemic aryllithium gives two atropdiastereoisomeric sulfoxides. Separation (by chromatography or crystallisation) and sulfoxide-lithium exchange of each diastereoisomer regenerates the aryllithium in enantiomerically pure form which can be quenched with a range of electrophiles with retention of stereochemical integrity. Overall the reaction sequence is a resolution but without the need for an acidic or basic substituent—a ‘traceless’ method. In certain instances, for example when the nucleophile is an ortholithiated peri-substituted 1-naphthamide, the diastereoisomeric sulfoxides may be interconverted thermally. This allows a dynamic resolution, under thermodynamic control, and hence in principle can give yields of the final products of greater than 50%. The utility of the method is demonstrated by the synthesis of a known atropisomeric phosphine ligand.     

Homolytic Substitution at the Sulfur Atom as a Tool for Organic Synthesis

The use of intramolecular homolytic substitution at the sulfur atom by aryl and vinyl radicals, as an alternative to the use of alkyl halides, and chalcogenides as radical precursors in organic synthesis is reviewed.     

Bioinspired Total Synthesis of Bipolarolides A and B

We have achieved the first total synthesis of bipolarolides A and B, which possess an intriguing and complex 5/6/6/6/5 caged pentacyclic skeleton with seven contiguous stereocenters. The synthesis features a lithium-halogen exchange/intermolecular nucleophilic addition to link two enantioenriched fragments, two ring-closing metathesis reactions to assemble the five- and eight-membered rings, and a bioinspired Prins reaction/ether formation cascade cyclization to construct the 5/6/6/6/5 caged skeleton.     

Asymmetric Synthesis of Chiral Sulfimides through the O-Alkylation of Enantioenriched Sulfinamides and Addition of Carbon Nucleophiles

Chiral sulfimides, the aza-analogues of sulfoxides, are valuable compounds in organic synthesis and medicinal chemistry. Herein, we report an efficient method for preparing chiral sulfimides from easily available enantioenriched sulfinamides. The key step of this method is a stereospecific oxygen-selective alkylation of enantioenriched sulfinamides, which is accomplished by using isopropyl iodide, K₂CO₃, and DMPU. The resulting chiral sulfinimidate esters are transformed to chiral sulfimides by the nucleophilic addition of the Grignard reagents under simple conditions. This transformation enables access to the enantioenriched diaryl or dialkyl sulfimides bearing two similar carbon substituents, which are difficult to synthesize by previous methods.     

Synthesis of Neocaesalpin A,AA, and Nominal Neocaesalpin K**

The first total synthesis of heavily oxidized cassane-type diterpenoid neocaesalpin A ( 1 ) is disclosed. At the heart of the synthesis lies an intermolecular Diels–Alder reaction that rapidly assembles the target framework from commercial materials. A carefully orchestrated sequence of oxidations secured the desired oxygenation pattern. Late-stage release of the characteristic butenolide occurred through a novel mercury(II)-mediated furan oxidation. Successful extension of the route allowed preparation of neocaesalpin AA ( 2 ) as well as nominal neocaesalpin K ( 3 ) and suggested structural revision of neocaesalpin K, leading to the hypothesis that the two are likely the same natural product with correct assignment as 2 .     

Facile Access to Cyclopropylboronates via Stereospecific Deborylative Cyclization: A Leaving Group-Assisted Activation of Geminal Diborons

Herein we reported a transition metal-free deborylative cyclization strategy, based on which two routes have been developed, generating racemic and enantioenriched cyclopropylboronates. The cyclization of geminal-bis(boronates) bearing a leaving group was highly diastereoselective, tolerating a few functional groups and applicable to heterocycles. When optically active epoxides were used as the starting materials, enantioenriched cyclopropylboronates could be efficiently prepared with >99 % stereospecificity. Mechanistic studies showed that the leaving group at the γ-position played a crucial role and significantly promoted the activation of the gem-diboron moiety.     

Understanding Electrochemical Reaction Mechanisms of Sulfur in All-Solid-State Batteries through Operando and Theoretical Studies **

Due to its outstanding safety and high energy density, all-solid-state lithium-sulfur batteries (ASLSBs) are considered as a potential future energy storage technology. The electrochemical reaction pathway in ASLSBs with inorganic solid-state electrolytes is different from Li-S batteries with liquid electrolytes, but the mechanism remains unclear. By combining operando Raman spectroscopy and ex situ X-ray absorption spectroscopy, we investigated the reaction mechanism of sulfur (S₈) in ASLSBs. Our results revealed that no Li₂S_8, Li₂S_6, and Li₂S₄ were formed, yet Li₂S₂ was detected. Furthermore, first-principles structural calculations were employed to disclose the formation energy of solid state Li₂S_n (1≤n≤8), in which Li₂S₂ was a metastable phase, consistent with experimental observations. Meanwhile, partial S₈ and Li₂S₂ remained at the full lithiation stage, suggesting incomplete reaction due to sluggish reaction kinetics in ASLSBs.     

A Single-Component Dual Donor Enables Ultrasound-Triggered Co-release of Carbon Monoxide and Hydrogen Sulfide

The development of dual gasotransmitter donors can not only provide robust tools to investigate their subtle interplay under pathophysiological conditions but also optimize therapeutic efficacy. While conventional strategies are heavily dependent on multicomponent donors, we herein report an ultrasound-responsive water-soluble copolymer ( PSHF ) capable of releasing carbon monoxide (CO) and hydrogen sulfide (H₂S) based on single-component sulfur-substituted 3-hydroxyflavone (SHF) derivatives. Interestingly, sulfur substitution can not only greatly improve the ultrasound sensitivity but also enable the co-release of CO/H₂S under mild ultrasound irradiation. The co-release of CO/H₂S gasotransmitters exerts a bactericidal effect against Staphylococcus aureus and demonstrates anti-inflammatory activity in lipopolysaccharide-challenged macrophages. Moreover, the excellent tissue penetration of ultrasound irradiation enables the local release of CO/H₂S in the joints of septic arthritis rats, exhibiting superior therapeutic efficacy without the need for any antibiotics.     

Total Synthesis and Structural Plasticity of Kratom Pseudoindoxyl Metabolites**

Mitragynine pseudoindoxyl, a kratom metabolite, has attracted increasing attention due to its favorable side effect profile as compared to conventional opioids. Herein, we describe the first enantioselective and scalable total synthesis of this natural product and its epimeric congener, speciogynine pseudoindoxyl. The characteristic spiro-5-5-6-tricyclic system of these alkaloids was formed through a protecting-group-free cascade relay process in which oxidized tryptamine and secologanin analogues were used. Furthermore, we discovered that mitragynine pseudoindoxyl acts not as a single molecular entity but as a dynamic ensemble of stereoisomers in protic environments; thus, it exhibits structural plasticity in biological systems. Accordingly, these synthetic, structural, and biological studies provide a basis for the planned design of mitragynine pseudoindoxyl analogues, which can guide the development of next-generation analgesics.