Photo-induced transition-metal and photosensitizer free cross–coupling of aryl halides with disulfides

Synthesis of 2,4-Disubstituted Oxazoles and Thiazoles via Brønsted Acid-Catalyzed Cyclization of α-diazoketones with Amides

A novel method is described for the synthesis of 2,4-disubstituted oxazole and thiazole derivates via the coupling of α-diazoketones with (thio)amides or thioureas using trifluoromethanesulfonic acid (TfOH) as a catalyst. This protocol is characterized by mild reaction conditions, metal-free, and simplicity and also features good functional group tolerance, good to excellent yields, and a broad substrate scope with more than 40 examples. Experimental studies suggest a mechanism involving 2-oxo-2-phenylethyl trifluoromethanesulfonate as the key intermediate.

Photoredox Catalytic Installation of an Alkyl/Aryl Side Chain and Deuterium into (S)-Methyleneoxazolidinone: Synthesis of Enantioenriched α-Deuterated α-Amino Acid Derivatives

A photoredox catalytic asymmetric method has been established for the installation of both aliphatic and aromatic side chains and the introduction of deuterium into the chiral methyleneoxazolidinone simultaneously. Efficient coupling of readily available boronic acids with the chiral auxiliary delivers structurally diverse α-deuterated α-amino acid derivatives with a high level of diastereoselectivity and deuteration.

Organophosphorus-Catalyzed "Dual-Substrate Deoxygenation" Strategy for C-S Bond Formation from Sulfonyl Chlorides and Alcohols/Acids

A green method to construct C-S bonds using sulfonyl chlorides and alcohols/acids via a P^III/P^V═O catalytic system is reported. The organophosphorus-catalyzed umpolung reaction promotes us to propose the "dual-substrate deoxygenation" strategy. Herein, we adopt the "dual-substrate deoxygenation" strategy, which achieves the deoxygenation of sulfonyl chlorides and alcohols/acids to synthesize thioethers/thioesters driven by P^III/P^V═O redox cycling. The catalytic method represents an operationally simple approach using stable phosphine oxide as a precatalyst and shows broad functional group tolerance. The potential application of this protocol is demonstrated by the late-stage diversification of drug analogues.

Catalytic [2,3]-sigmatropic rearrangement of sulfonium ylides derived from azoalkenes: non-carbenoid Doyle-Kirmse reaction

The Sc(III)-catalyzed [2,3]-sigmatropic rearrangement of sulfonium ylides derived from azoalkenes has been established. Owing to the absence of a carbenoid intermediate, this protocol represents the first non-carbenoid variant of the Doyle-Kirmse reaction. Under mild conditions, a variety of tertiary thioethers have been readily prepared in good to excellent yields.

Metal-free photo-induced sulfidation of aryl iodide and other chalcogenation

A photo-induced C-S radical cross-coupling of aryl iodides and disulfides under transition-metal and external photosensitizer free conditions for the synthesis of aryl sulfides at room temperature has been presented, which features mild reaction conditions, broad substrate scope, high efficiency, and good functional group compatibility. The developed methodology could be readily applied to forge C-S bond in the field of pharmaceutical and material science.

Visible-light-induced cross-coupling of aryl iodides with hydrazones via an EDA-complex

A visible-light-induced, transition-metal and photosensitizer-free cross-coupling of aryl iodides with hydrazones was developed. In this strategy, hydrazones were used as alternatives to organometallic reagents, in the absence of a transition metal or an external photosensitizer, making this cross-coupling mild and green. The protocol was compatible with a variety of functionalities, including methyl, methoxy, trifluoromethyl, halogen, and heteroaromatic rings. Mechanistic investigations showed that the association of the hydrazone anion with aryl halides formed an electron donor–acceptor complex, which when excited with visible light generated an aryl radical via single-electron transfer.

Visible-light-induced catalyst-free cross-coupling of aryl iodides with hydrazones via single-electron-transfer was reported. The mechanistic investigations showed that the association of hydrazone anion with aryl iodides formed an EDA complex.

Atom- and step-economic 1,3-thiosulfonylation of activated allenes with thiosulfonates to access vinyl sulfones/sulfides

A new type of organocatalyzed 1,3-thiosulfonylation has been developed to straightforwardly access highly functionalized vinyl sulfones, which features mild conditions, atom- and step-economy, practicability, conciseness, and environmental friendliness. Moreover, these valuable products can be transformed to vinyl sulfides via a base-promoted isomerization. The versatile route can efficiently and rapidly introduce SCD₃ groups with excellent levels of deuterium content (>99% D) by utilizing our newly developed SCD₃ reagents. Gram-scale operations and further transformations are smoothly carried out, providing promising applications for drug discovery.

Water Mediated Direct Thioamidation of Aldehydes at Room Temperature

A mild, greener approach toward thioamide synthesis has been developed. Its unique features include water-mediated reaction with no input energy, additives, or catalysts as well. The presented protocol is attractive with readily available starting materials and the use of different array amines, along with a scaled-up method. Biologically active molecules such as thionicotinamide and thioisonicotinamide can be synthesized from this procedure.

Visible-light-induced transition metal and photosensitizer free decarbonylative addition of amino-arylaldehydes to ketones

The decarbonylative-coupling reaction is generally promoted by transition metals (via organometallic complexes) or peroxides (via radical intermediates), often at high temperatures to facilitate the CO release. Herein, a visible-light-induced, transition metal and external photosensitizer free decarbonylative addition of benzaldehydes to ketones/aldehydes at room temperature is reported. Tertiary/secondary alcohols were obtained in moderate to excellent yields promoted by using CsF under mild conditions. The detailed mechanistic investigation showed that the reaction proceeded through photoexcitation–decarbonylation of the aldehyde to generate an aromatic anion, followed by its addition to ketones/aldehydes. The reaction mechanism was verified by the density functional theory (DFT) calculations.

A visible-light-induced, transition-metal and external photosensitizer free decarbonylative addition of benzaldehydes to ketones/aldehydes via anion intermediates at room temperature is developed.

Site-Selective Synthesis of Aryl Sulfides via Oxidative Aromatization of Cyclohexanones with Thiophenols

We have introduced a metal-free facile access for the thiolation/aromatization of cyclohexanones with thiophenols to the corresponding aryl sulfides. The dehydroaromatic reaction of non-aromatic cyclohexanones proceeded smoothly using oxygen as a green oxidant.

Photoinduced transition-metal and external photosensitizer free cross-coupling of aryl triflates with trialkyl phosphites

Photoinduced phosphonation of aryl triflates with trialkyl phosphites via a tandem single-electron-transfer, C-O bond cleavage and Arbuzov rearrangement process in the absence of transition-metal and external photosensitizer is reported herein. The protocol features good functional group compatibility and mild reaction conditions, providing various aryl phosphates in good to high yields. Furthermore, this strategy allows the late-stage phosphonation of complex and biologically active compounds.

Aerobic Cross-Dehydrogenative Coupling Reactions for Selective Mono- and Dithiolation of Phenols

A highly efficient strategy for the direct thiolation of phenols under transition metal-free and solvent-free conditions has been developed. These reactions are operationally simple with employing air (molecular oxygen) as an ideal oxidant and can selectively provide mono- and dithiolation products in good to excellent yields under basic conditions. The reaction tolerates a broad range of aryl thiols and arenes and is especially applicable for large-scale synthesis.

Photo-induced transition-metal and external photosensitizer-free organic reactions

Photoreactions have become powerful synthetic tools with a broad scope of applications. This review mainly focuses on photoreactions in the absence of transition-metals and photosensitizers, and highlights the mechanisms of such reactions.