Suzuki–Miyaura Cross-Coupling of Sulfoxides

Recent trends in incorporation of CO2 into organosulfur compounds via C-S bond cleavage

Desulfurative functionalization of organosulfur compounds to form various carbon-carbon and carbon-heteroatom bonds has become established as a powerful tool in organic chemistry. In this context, desulfurative carboxylation of this class of compounds using carbon dioxide (CO2) as a sustainable and renewable source of carboxyl has recently been developed as an efficient option for the synthesis of carboxylic acid derivatives. The aim of this Focus Review is to summarize the major progress in this appealing research field with particular emphasis on the mechanistic features of the reactions. Literature has been surveyed until the end of February 2024, according to the data collected using SciFinder and Google Scholar engines.

Nickel-Catalyzed Cross-Coupling Reaction of Aryl Methyl Sulfides with Aryl Bromides

A nickel-catalyzed cross-coupling reaction of aryl methyl sulfides with aryl bromides has been developed to access biaryls in yields of up to 86%. The reactions proceeded well using Ni(COD)2 as catalyst with the ligand BINAP (2,2'-bis(diphenylphosphanyl)-1,1'-binaphthalene) in the presence of magnesium. The method has a broad scope of substrates and is scalable. The wide availability of commercially available aryl bromides and the absence of preparation and preparation of organometallic reagents make the reaction of high application value.

Pd-NHC catalysed regioselective activation of B(3,6)-H of o-carborane - a synergy between experiment and theory

Regioselective B-H activation of o-carboranes is an effective way for constructing o-carborane derivatives, which have broad applications in medicine, catalysis and the wider chemical industry. However, the mechanistic basis for the observed selectivities remains unresolved. Herein, a series of density functional theory (DFT) calculations were employed to characterise the palladium N-heterocyclic carbene (Pd-NHC) catalysed regioselective B(3,6)-diarylation of o-carboranes. Computational results at the IDSCRF(ether)-LC-ωPBE/BS1 and IDSCRF(ether)-LC-ωPBE/BS2 levels showed that the reaction undergoes a Pd(0) → Pd(II) → Pd(0) oxidation/reduction cycle, with the regioselective B(3)-H activation being the rate-determining step (RDS) for the full reaction profile. The computed RDS free energy barrier of 24.3 kcal mol-1 agrees well with the 82% yield of B(3,6)-diphenyl-o-carborane in ether solution at 298 K after 24 hours of reaction. The Ag2CO3 additive was shown to play a crucial role in lowering the RDS free energy barrier and facilitating the reaction. Natural charge population (NPA) and molecular surface electrostatic potential (ESP) analyses successfully predicted the experimentally observed regioselectivities, with electronic effects being revealed to be the dominant contributors to product selectivity. Steric hindrance was also shown to impact the reaction rate, as revealed by experimental and computational characterisation studies of substituents and ligand effects. Furthermore, computational predictions aligned with the experimental findings that NHC ligands outperform the phosphine ones for this particular reaction. Overall, the observed trends reported in this work are expected to assist in the rational optimisation of the efficiency and regioselectivity of this and related reactions.

Manipulation of an electron by photoirradiation in the electron-catalyzed cross-coupling reaction

An electron has recently been shown to catalyze the cross-coupling reaction of organometallic compounds with aryl halides. In terms of green and sustainable chemistry, the electron catalysis is much more desirable than the inevitably used transition metal catalysis but a high temperature of more than 100°C is required to achieve it. Here, we disclose that visible light photoirradiation accelerates the electron-catalyzed reaction of arylzinc reagents with aryl halides with the aid of a photoredox catalysis. Photoexcitation of a photoredox catalyst and an anion radical intermediate respectively affects the supply and transfer of the electron catalyst, promoting the cross-coupling reaction to proceed at room temperature. The supply of the electron catalyst by the photoredox catalysis makes the scope of aryl halides wider.

Mechanistic views and computational studies on transition-metal-catalyzed reductive coupling reactions

Transition-metal-catalyzed reductive coupling reactions have been considered as a powerful tool to convert two electrophiles into value-added products. Numerous related reports have shown the fascinating potential. Mechanistic studies, especially theoretical studies, can provide important implications for the design of novel reductive coupling reactions. In this review, we summarize the representative advancements in theoretical studies on transition-metal-catalyzed reductive coupling reactions and systematically elaborate the mechanisms for the key steps of reductive coupling reactions. The activation modes of electrophiles and the deep insights of selectivity generation are mechanistically discussed. In addition, the mechanism of the reduction of high-oxidation-state catalysts and further construction of new chemical bonds are also described in detail.

Organothianthrenium salts: synthesis and utilization

Organothianthrenium salts are a class of compounds containing a positively charged sulfur atom and a neutral sulfur atom. Over the past years, organothianthrenium salts have been emerging as attractive precursors for a myriad of transformations to forge new C-C and C-X bonds due to their unique structural characteristics and chemical behaviors. The use of the thianthrenation strategy selectively transforms C-H, C-O, and other chemical bonds into organothianthrenium salts in a predictable manner, providing a straightforward alternative for regioselective functionalizations for arenes, alkenes, alkanes, alcohols, amines and so on through diverse reaction mechanisms under mild conditions. In this review, the preparation of different organothianthrenium salts is summarized, including aryl, alkenyl and alkyl thianthrenium salts. Moreover, the utilization of organothianthrenium salts in different catalytic processes and their synthetic potentials are also discussed.

Synthesis and Properties of Pyridine-Fused Triazolylidene-Palladium: Catalyst for Cross-Coupling Using Chloroarenes and Nitroarenes

The synthesis and catalytic activity of pyridine-fused triazolylidene as a novel abnormal N-heterocyclic carbene (aNHC) ligand is described. The evaluation of physical properties using X-ray crystallographic analysis and infrared spectroscopy revealed that these triazolylidenes have a high electron-donating ability toward the metal center. The application of this triazolylidene to the palladium-catalyzed cross-coupling of chloroarenes and nitroarenes with arylboronic acids showcased its ability to activate C-Cl and C-NO₂ bonds.

Nickel-Catalyzed Direct Cross-Coupling of Diaryl Sulfoxide with Aryl Bromide

The direct cross-couplings of diaryl sulfoxides with aryl bromides via C-S bond cleavage could be readily accomplished using nickel(II) as the catalyst, 1,2-bis(diphenylphosphino)ethane (dppe) as the ligand, and magnesium turnings as the reducing metal in THF, leading to the corresponding biaryls in moderate to good yields. The reaction exhibited a broad substrate scope and could be applied to a gram-scale synthesis. The "one-pot" reaction, which avoids the utility of presynthesized and moisture-labile organometallic compounds, is operationally simple and step-economic.

Room-Temperature Synthesis of 1,3,5-Tri(het)aryl Benzene from Nitroalkenes Using Pd(OAc)2: Complete Mechanistic and Theoretical Studies

Herein, a room-temperature catalytic pathway for 1,3,5-tri(het)aryl derivatives from nitroalkenes using simple Pd(OAc)₂ is presented. This newly developed C-C bond-forming methodology takes place in a cascade manner with the initial pallado-Morita-Baylis-Hillman (MBH) type adduct. The broad substrate scopes, functional group tolerance, and different aryl-substituted benzene derivatives make this methodology more attractive. Furthermore, the mechanistic understanding through isolation of intermediates and DFT studies of the catalytic cycle provide requisite insight into the methodology.

Chromium-catalyzed couplings of C(aryl)-SMe bonds for accessing arylated and alkylated benzaldehyde derivatives

Described here is the chromium-catalyzed cleavage of C(aryl)-SMe bonds leading to coupling with organomagnesium to give functionalized benzaldehydes under mild conditions. This reaction was promoted specifically by a low-cost and simple CrCl₂ salt used as a precatalyst, enabling synchronous activations of ortho-C(aryl)-SMe and ortho'-C(aryl)-H bonds to achieve difunctionalization of benzaldimines. This work provided a strategy for accessing arylated, alkylated, and diarylated benzaldehyde derivatives as a result of the couplings of C(aryl)-SMe and C(aryl)-SMe/C(aryl)-H bonds promoted with cost-effective Cr catalysis.

‘Awaken’ aryl sulfonyl fluoride: a new partner in the Suzuki–Miyaura coupling reaction

An example of the activation of the –SO2F group, which is traditionally considered a stable group even in the presence of a transition metal, is described using a novel partner in the Suzuki–Miyaura coupling reaction catalyzed by Pd(OAc)2 and Ruphos as ligands.

Desulfonative Suzuki-Miyaura Coupling of Sulfonyl Fluorides

Sulfonyl fluorides have emerged as powerful "click" electrophiles to access sulfonylated derivatives. Yet, they are relatively inert towards C-C bond forming transformations, notably under transition-metal catalysis. Here, we describe conditions under which aryl sulfonyl fluorides act as electrophiles for the Pd-catalyzed Suzuki-Miyaura cross-coupling. This desulfonative cross-coupling occurs selectively in the absence of base and, unusually, even in the presence of strong acids. Divergent one-step syntheses of two analogues of bioactive compounds showcase the expanded reactivity of sulfonyl fluorides to encompass both S-Nu and C-C bond formation. Mechanistic experiments and DFT calculations suggest oxidative addition occurs at the C-S bond followed by desulfonation to form a Pd-F intermediate that facilitates transmetalation.

Arylketones as Aryl Donors in Palladium-Catalyzed Suzuki-Miyaura Couplings

Herein, we report the arylation, alkylation, and alkenylation of aryl ketones via a palladium-catalyzed Suzuki-Miyaura cross-coupling reaction. The use of the pyridine-oxazoline ligand is the key to the cleavage of the unstrained C-C bond. The late-stage arylation of aryl ketones derived from drugs and natural products demonstrated the synthetic utility of this protocol.

Sulfoxide and Sulfone Synthesis via Electrochemical Oxidation of Sulfides

The oxidation of diaryl sulfides and aryl alkyl sulfides to the corresponding sulfoxides and sulfones under electrochemical conditions is reported. Sulfoxides are selectively obtained in good yield under a constant current of 5 mA for 10 h in DMF, while sulfones are formed as the major product under a constant current of 10 or 20 mA for 10 h in MeOH. The oxygen of both the sulfoxide and sulfone function is derived from water.

A Practice of Reticular Chemistry: Construction of a Robust Mesoporous Palladium Metal-Organic Framework via Metal Metathesis

Constructing stable palladium(II)-based metal-organic frameworks (MOFs) would unlock more opportunities for MOF chemistry, particularly toward applications in catalysis. However, their availability is limited by synthetic challenges due to the inertness of the Pd-ligand coordination bond, as well as the strong tendency of the Pd(II) source to be reduced under typical solvothermal conditions. Under the guidance of reticular chemistry, herein, we present the first example of an azolate Pd-MOF, BUT-33(Pd), obtained via a deuterated solvent-assisted metal metathesis. BUT-33(Pd) retains the underlying sodalite network and mesoporosity of the template BUT-33(Ni) and shows excellent chemical stability (resistance to an 8 M NaOH aqueous solution). With rich Pd(II) sites in the atomically precise distribution, it also demonstrates good performances as a heterogeneous Pd(II) catalyst in a wide application scope, including Suzuki/Heck coupling reactions and photocatalytic CO₂ reduction to CH₄. This work highlights a feasible approach to reticularly construct noble metal based MOFs via metal metathesis, in which various merits, including high chemical stability, large pores, and tunable functions, have been integrated for addressing challenging tasks.

Synthesis of 2-Aryl-4H-thiochromen-4-one Derivatives via a Cross-Coupling Reaction

A concise and efficient cross-coupling synthetic strategy has been developed to construct 2-aryl-4H-thiochromen-4-one derivatives from 2-sulfinyl-thiochromones and arylboronic acids. This reaction proceeds via a catalyst system of Lewis acid and palladium(II) combined with XPhos as an optimal ligand in moderate to good yields. Besides, this flexible methodology provides a wide scope for the synthesis of different functionally substituted thiochromone scaffolds and can be further exploited to construct diverse thioflavone libraries for pharmaceutical research.

Ni-Catalyzed Borylation of Aryl Sulfoxides

A nickel/N-heterocyclic carbene (NHC) catalytic system has been developed for the borylation of aryl sulfoxides with B2 (neop)2 (neop=neopentyl glycolato). A wide range of aryl sulfoxides with different electronic and steric properties were converted into the corresponding arylboronic esters in good yields. The regioselective borylation of unsymmetric diaryl sulfoxides was also feasible leading to borylation of the sterically less encumbered aryl substituent. Competition experiments demonstrated that an electron-deficient aryl moiety reacts preferentially. The origin of the selectivity in the Ni-catalyzed borylation of electronically biased unsymmetrical diaryl sulfoxide lies in the oxidative addition step of the catalytic cycle, as oxidative addition of methoxyphenyl 4-(trifluoromethyl)phenyl sulfoxide to the Ni(0) complex occurs selectively to give the structurally characterized complex trans-[Ni(ICy)2 (4-CF3 -C6 H4 ){(SO)-4-MeO-C6 H4 }] 4. For complex 5, the isomer trans-[Ni(ICy)2 (C6 H5 )(OSC6 H5 )] 5-I was structurally characterized in which the phenyl sulfinyl ligand is bound via the oxygen atom to nickel. In solution, the complex trans-[Ni(ICy)2 (C6 H5 )(OSC6 H5 )] 5-I is in equilibrium with the S-bonded isomer trans-[Ni(ICy)2 (C6 H5 )(SOC6 H5 )] 5, as shown by NMR spectroscopy. DFT calculations reveal that these isomers are separated by a mere 0.3 kJ/mol (M06/def2-TZVP-level of theory) and connected via a transition state trans-[Ni(ICy)2 (C6 H5 )(η2 -{SO}-C6 H5 )], which lies only 10.8 kcal/mol above 5.

(Trifluoromethoxy)Phenylboronic Acids: Structures, Properties, and Antibacterial Activity

Three isomers of (trifluoromethoxy)phenylboronic acids were studied in the context of their physicochemical, structural, antimicrobial and spectroscopic properties. They were characterized by ¹H, ¹³C, ¹¹B and ¹⁹F NMR spectroscopy. The acidity of all the isomers was evaluated by both spectrophotometric and potentiometric titrations. The introduction of the -OCF₃ group influences the acidity, depending, however, on the position of a substituent, with the ortho isomer being the least acidic. Molecular and crystal structures of ortho and para isomers were determined by the single crystal XRD method. Hydrogen bonded dimers are the basic structural motives of the investigated molecules in the solid state. In the case of the ortho isomer, intramolecular hydrogen bond with the -OCF₃ group is additionally formed, weaker, however, than that in the analogous -OCH₃ derivative, which has been determined by both X-Ray measurements as well as theoretical DFT calculations. Docking studies showed possible interactions of the investigated compounds with LeuRS of Escherichia coli. Finally, the antibacterial potency of studied boronic acids in vitro were evaluated against Escherichia coli and Bacillus cereus.

Synthesis and reactivity of boryloxorhodium complexes. Relevance to intermolecular transmetalation from boron to rhodium in Rh-catalyzed reactions

The synthesis of a dimeric boryloxorhodium complex having the Rh-O-Bpin scaffold from the reaction of [(cod)Rh(OMe)]2 or [(cod)Rh(OH)]2 with an arylboronate has been achieved. The obtained dirhodium complex is converted into mononuclear complex [(cod)Rh(OBpin)(PPh3)], which reacts with arylboronic acid to afford the complex with an Rh-aryl bond via transmetalation from boron to rhodium. The dimeric boryloxorhodium complex catalyzes the 1,4-addition of arylboronic acid to cyclohexene-2-one.

Palladium catalyzed desulfurative coupling of allyl sulfides with organoboronic acids

A palladium catalyzed desulfurative coupling of allylthioethers with organoboronic acids under mild reaction conditions is described.