Overriding Cage Effect in Electron Donor-Acceptor Photoactivation of Diaryliodonium Reagents: Synthesis of Chalcogenides

In recent times, diaryliodonium reagents (DAIRs) have witnessed a resurgence as arylating reagents, especially under photoinduced conditions. However, reactions proceeding through electron donor-acceptor (EDA) complex formation with DAIRs are restricted to electron-rich reacting partners serving as donors due to the well-known cage effect. We discovered a practical and high-yielding visible-light-induced EDA platform to generate aryl radicals from the corresponding DAIRs and use them to synthesize key chalcogenides. In this process, an array of DAIRs and dichalcogenides react in the presence of 1,4 diazabicyclo[2.2.2]octane (DABCO) as a cheap and readily available donor, furnishing a variety of di(hetero)aryl and aryl/alkyl chalcogenides in good yields. The method is scalable, features a broad scope with good yields, and operates under open-to-air conditions. The photoinduced chalcogenation technology is suitable for late-stage functionalizations and disulfide bioconjugations and facilitates access to biologically relevant thioesters, dithiocarbamates, sulfoximines, and sulfones. Moreover, the method applies to synthesizing diverse pharmaceuticals, such as vortioxetine, promazine, mequitazine, and dapsone, under amenable conditions.

Cu(II)-Catalyzed Hydroboration Reactions of 1,1-Disubstituted α,β-Unsaturated Ketones, Esters, and Amides in Pure Water

Here, a Cu2(OH)2CO3-catalyzed hydroboration reaction of 1,1-disubstituted α,β-unsaturated compounds has been developed. The reaction was carried out using water as a solvent at room temperature except for N-monosubstituted α,β-unsaturated amides. This method is applicable to diverse 1,1-disubstituted α,β-unsaturated ketones, esters, and amides, showing excellent reactivity (up to 98% yield). Gram-scale experiments and functional group transformations further demonstrated the practicality of this method.

Mechanochemical Nickel-Catalyzed Carbon-Sulfur Bond Formation between Aryl Iodides and Aromatic Sulfur Surrogates

The formation of aromatic thioethers from C-S coupling is of great importance in synthetic chemistry. Traditional solution strategies through transition-metal catalysis generally require bulk solution, heat, and longer reaction time. Herein, a mechano-promoted sulfenylation of aryl iodides with nickel catalysis is described. The active aromatic sulfide agents are in-situ generated from aromatic thiol or disulfide and subsequently adapted in the nickel catalytic cycle, with a tolerance of broad substituted groups under optimized conditions. In addition to the gram-scale synthesis that reveals the application potential of the method, the radical trapping and competitive experiments are also conducted for the mechanistic study, thus providing a plausible mechanism rationally. Furthermore, the proposed methodology is certificated as being versatile and following the green principles with ideal calculated values of green chemistry metrics, and the comparison with other approaches for C-S bond formation is also demonstrated.

One-Pot Synthesis of Benzoxazole/Benzothiazole-Substituted Esters by Michael Addition: A Selective Construction of C-N/C-S Bonds

An efficient and convenient synthesis of benzoxazole/benzothiazole-substituted esters in a one-pot strategy is reported. In this investigation, a selective construction of C-N and C-S bonds via simple addition is performed. Thus, using substituted 2-aminophenols/2-aminobenzenethiols, TMTD (tetramethylthiuram disulfide) and α,β-unsaturated esters as starting substrates, C-N and C-S bonds can be selectively constructed by means of the Michael addition reaction. This protocol features high selectivity, high atomic economy, mild conditions, good functional tolerance and good to excellent yields, showing the potential value for the preparation of some biologically and pharmaceutically active compounds.

Ni-catalyzed C-S bond construction and cleavage

Sulfur-containing compounds have attracted considerable interest due to their wide-ranging applications in pharmaceuticals, agriculture, natural products, and organic materials. The development of efficient and rapid methods for the construction and transformation of sulfur-containing compounds is of great importance. Since nickel is inexpensive and has a variety of valence states, strong nucleophilicity and low energy barriers for oxidative addition, the construction and transformation of sulfur-containing compounds by nickel-catalyzed cross-coupling have become important strategies. In addition, sulfur-containing compounds have also been playing increasingly important roles in the field of cross-coupling due to their thermodynamically stable but dynamic activity. This review will focus on nickel-catalyzed construction and transformation of various sulfide-containing compounds, such as sulfides, disulfides, and hypervalent sulfur-containing compounds.

Rapid Photoracemization of Chiral Alkyl Aryl Sulfoxides

The photoracemization of chiral alkyl aryl sulfoxides with a photosensitizer has not been sufficiently investigated thus far. Therefore, in this study, a rapid photoracemization reaction of enantiopure alkyl aryl sulfoxides using 1 mol % 2,4,6-triphenylpyrylium tetrafluoroborate (TPT⁺) was developed. Various substitution patterns were tolerated and every racemization reaction proceeded extremely fast (k₂ = 1.77 × 10⁴-6.08 × 10¹ M^-1 s^-1, t_1/2 = 0.4-114 s). Some chiral sulfoxides with easily oxidizable functional groups are not appropriate for this photoisomerization. The electrochemical potentials of the functional groups, determined via cyclic voltammetry, are useful for predicting the reactive or nonreactive groups in this photoracemization reaction. A theoretical study was conducted to clarify the sp²-like nature of S of the sulfoxide cation radical, which makes photoracemization easier.

Rh(I)-Catalyzed Intramolecular Decarbonylation of Thioesters

Decarbonylative synthesis of thioethers from thioesters proceeds in the presence of a catalytic amount of [Rh(cod)Cl]₂ (2 mol %). The protocol represents the first Rh-catalyzed decarbonylative thioetherification of thioesters to yield valuable thioethers. Notable features include the absence of phosphine ligands, inorganic bases, and other additives and excellent group tolerance to aryl chlorides and bromides that are problematic using other metals to promote decarbonylation. Gram scale synthesis, late-stage pharmaceutical derivatization, and orthogonal site-selective cross-couplings by C-S/C-Br cleavage are reported.

Nickel-Catalyzed Decarbonylative Thioetherification of Acyl Fluorides via C–F Bond Activation

Nickel-catalyzed decarbonylative thioetherification of acyl fluorides has been developed. This transformation allows an array of acyl fluorides to react with thiophenols. A wide range of functional groups are well tolerated and the corresponding sulfides can be obtained in good to excellent yields. This protocol provides the formation of diverse carbon–sulfur bonds via a highly efficient decarbonylative process.

Ligand-Free Copper(I)-Mediated Cross-Coupling Reactions of Organostannanes with Sulfur Electrophiles

The synthesis of aryl thioether through the cross-coupling of C-S bond is a highly attractive area of research due to the prevalence of aryl thioether in bioactive natural products, functional materials, agrochemicals, and pharmaceutically active compounds. Herein, we report a ligand-free Cu(I) mediated electrophilic thiolation of organostannanes with sulfur electrophiles. A selective transfer of alkyl groups was achieved in reactions with alkyl carbastannatranes affording congested thioethers. This study offers a unified method to access diaryl and aryl alkyl thioethers and was demonstrated in the context of late-stage modifications..

Advances in Cu and Ni-catalyzed Chan–Lam-type coupling: synthesis of diarylchalcogenides, Ar2–X (X = S, Se, Te)

Advances in the Cu and Ni-catalyzed Chan–Lam-type coupling of aryl/heteroarylboronic acids with various chalcogen sources for diarylsulfide, diarylselenide and diaryltelluride synthesis are covered in this review.