Room-Temperature Arylation of Thiols: Breakthrough with Aryl Chlorides

The formation of aryl C−S bonds is an important chemical transformation because aryl sulfides are valuable building blocks for the synthesis of biologically and pharmaceutically active molecules and organic materials. Aryl sulfides have traditionally been synthesized through the transition-metal-catalyzed cross-coupling of aryl halides with thiols. However, the aryl halides used are usually bromides and iodides; readily available, low-cost aryl chlorides often not reactive enough. Furthermore, the deactivation of transition-metal catalysts by thiols has forced chemists to use high catalyst loadings, specially designed ligands, high temperatures, and/or strong bases, thus leading to high costs and the incompatibility of some functional groups. Herein, we describe a simple and efficient visible-light photoredox arylation of thiols with aryl halides at room temperature. More importantly, various aryl chlorides are also effective arylation reagents under the present conditions.     

Metal‐Free,Room‐Temperature,Radical Alkoxycarbonylation of Aryldiazonium Salts through Visible‐Light Photoredox Catalysis

The first radical alkoxycarboxylation of aryldiazonium salts using CO gas through visible‐light‐induced photoredox catalysis (16 W blue LEDs) has been developed. This reaction is entirely metal‐free, is carried out at room temperature with a low loading of an organic dye as a photocatalyst (0.5 mol %), and provides a wide range of arylcarboxylic acid esters in high yields. Importantly, this photocatalytic system can be successfully extended to other carboxylation reactions.     

Efficient Aryl Migration from an Aryl Ether to a Carboxylic Acid Group To Form an Ester by Visible‐Light Photoredox Catalysis

We have developed a highly efficient aryl migration from an aryl ether to a carboxylic acid group through retro‐Smiles rearrangement by visible‐light photoredox catalysis at ambient temperature. Transition metals and a stoichiometric oxidant and base are avoided in the transformation. Inspired by the high efficiency of this transformation and the fundamental importance of C−O bond cleavage, we developed a novel approach to the C−O cleavage of a biaryl ether to form two phenolic compounds, as demonstrated by a one‐pot, two‐step gram‐scale reaction under mild conditions. The aryl migration exhibits broad scope and can be applied to the synthesis of pharmaceutical compounds, such as guacetisal. Primary mechanistic studies indicate that the catalytic cycle occurs by a reductive quenching pathway.     

Mild,Redox‐Neutral Formylation of Aryl Chlorides through the Photocatalytic Generation of Chlorine Radicals

We report a redox‐neutral formylation of aryl chlorides that proceeds through selective 2‐functionalization of 1,3‐dioxolane through nickel and photoredox catalysis. This scalable benchtop approach provides a distinct advantage over traditional reductive carbonylation in that no carbon monoxide, pressurized gas, or stoichiometric reductant is employed. The mild conditions give unprecedented scope from abundant and complex aryl chloride starting materials.     

Room‐Temperature Gold‐Catalysed Arylation of Heteroarenes: Complementarity to Palladium Catalysis

Tailoring of the pre‐catalyst, the oxidant and the arylsilane enables the first room‐temperature, gold‐catalysed, innate C?H arylation of heteroarenes. Regioselectivity is consistently high and, in some cases, distinct from that reported with palladium catalysis. Tolerance to halides and boronic esters, in both the heteroarene and silane partners, provides orthogonality to Suzuki–Miyaura coupling.     

Merging Regiodivergent Catalysis with Atom‐Economical Radical Arylation

A titanocene‐catalyzed regiodivergent radical arylation is described that allows access to either enantiomerically pure tetrahydroquinolines or indolines from a common starting material. The regioselectivity of epoxide opening that results in the high selectivity of heterocycle formation is controlled by two factors, the absolute configuration of the enantiopure ligands of the (C₅H₄R)₂TiX₂ catalyst and the inorganic ligand X (X=Cl, OTs). The overall reaction is atom‐economical and constitutes a radical Friedel–Crafts alkylation.     

Structure of the Au23−xAgx(S‐Adm)15 Nanocluster and Its Application for Photocatalytic Degradation of Organic Pollutants

Ligands play an important role in determining the atomic arrangement within the metal nanoclusters. Here, we report a new nanocluster [Au_23?xAg_x(S‐Adm)₁₅] protected by bulky adamantanethiol ligands which was obtained through a one‐pot synthesis. The total structure of [Au_23?xAg_x(S‐Adm)₁₅] comprises an Au_13?xAg_x icosahedral core, three Au₃(SR)₄ units, and one AgS₃ staple motif in contrast to the 15‐atom bipyramidal core previously seen in [Au_23?xAg_x(SR)₁₆]. UV/Vis spectroscopy indicates that the HOMO–LUMO gap of [Au_23?xAg_x(S‐Adm)₁₅] is 1.5 eV. DFT calculations reveal that [Au₁₉Ag₄(S‐Adm)₁₅] is the most stable structure among all structural possibilities. Benefitting from Ag doping, [Au_23?xAg_x(S‐Adm)₁₅] exhibits drastically improved photocatalytic activity for the degradation of rhodamine B (RhB) and phenol under visible‐light irradiation compared to Au₂₃ nanoclusters.     

Visible Light‐Induced Room‐Temperature Heck Reaction of Functionalized Alkyl Halides with Vinyl Arenes/Heteroarenes

The first visible light‐induced Pd‐catalyzed Heck reaction of α‐heteroatom substituted alkyl iodides and ‐bromides with vinyl arenes/heteroarenes has been developed. This transformation efficiently proceeds at room temperature and enables synthesis of valuable functionalized allylic systems, such as allylic silanes, boronates, germanes, stannanes, pivalates, phosphonates, phthalimides, and tosylates from the corresponding α‐substituted methyl iodides. Notably, synthesis of the latter substrates failed under existing thermally induced Pd‐catalyzed conditions, which highlights the importance of visible light for this transformation.     

Visible‐Light‐Driven N‐Heterocyclic Carbene Catalyzed γ‐ and ϵ‐Alkylation with Alkyl Radicals

The merging of photoredox catalysis and N‐heterocyclic carbene (NHC) catalysis for γ‐ and ?‐alkylation of enals with alkyl radicals was developed. The alkylation reaction of γ‐oxidized enals with alkyl halides worked well for the synthesis γ‐multisubstituted‐α,β‐unsaturated esters, including those with challenging vicinal all‐carbon quaternary centers. The synthesis of ?‐multisubstituted‐α,β‐γ,δ‐diunsaturated esters by an unprecedented NHC‐catalyzed ?‐functionalization was also established.     

C−O Activation by a Rhodium Bis(N‐Heterocyclic Carbene) Catalyst: Aryl Carbamates as Arylating Reagents in Directed C−H Arylation

Despite recent progress in the catalytic transformation of inert phenol derivatives as alternatives to aryl halides and triflates, attempts at the cross‐coupling of inert phenol derivatives with the C−H bonds of arenes have met with limited success. Herein, we report the rhodium‐catalyzed cross‐coupling of aryl carbamates with arenes bearing a convertible directing group. The key to success is the use of an in situ generated rhodium bis(N‐heterocyclic carbene) species as the catalyst, which can promote activation of the inert C(sp²)−O bond in aryl carbamates.     

Microwave‐Assisted Palladium‐Catalyzed Direct Arylation of 1,4‐Disubstituted 1,2,3‐Triazoles with Aryl Chlorides

Treatment of 1,4‐disubstituted 1,2,3‐triazoles with aryl chlorides in the presence of potassium carbonate under palladium catalysis and microwave irradiation at 250 °C for 15 min leads to arylation of the triazole at the 5‐position. A variety of functional groups, including ester and hydroxy groups, are compatible. The procedure is suitable for the regioselective preparation of trisubstituted triazoles. Microwave irradiation accelerates the reaction, thus allowing the rapid synthesis of trisubstituted triazoles, which are difficult to synthesize selectively.