Transition-Metal-Free Suzuki-Type Cross-Coupling Reaction of Benzyl Halides and Boronic Acids via 1,2-Metalate Shift

Chemo-, Regio-, and Stereoselective cis-Hydroboration of 1,3-Enynes: Copper-Catalyzed Access to (Z,Z)- and (Z,E)-2-Boryl-1,3-dienes

A copper-catalyzed alkyne-selective hydroboration of 1,3-enynes is disclosed, providing access to the previously elusive 2-boryl-1,3-dienes. Using CuOAc, Xantphos, and HBpin, Bpin was installed on the internal carbon of a series of symmetric and nonsymmetric 1,3-enynes, affording products with excellent Z:E selectivity. The utility of the 2-boryl-1,3-diene products was demonstrated by transformation to useful functional groups.

Light-induced arylation (alkylation) of N-sulfonylhydrazones with boronic acids

Di- and triarylmethanes are an important class of compounds in many fields. Here, we report an efficient light-induced arylation (alkylation) for the synthesis of diarylmethanes, bis(diarylmethyl)benzenes, arylalkylmethanes, and triarylmethanes from readily accessible N-sulfonylhydrazones and aryl/alkylboronic acids with the aid of Cs2CO3. In the presence of light, the synthesis of diarylmethanes was also achieved from aldehydes in a one-pot manner via a three-component approach in good yields. Furthermore, we have demonstrated the synthetic utility by synthesizing organoboron compounds and 2°-alcohol.

One-Pot, Three-Component Assembly of Sulfides Using a Sulfoxide Reagent as a Sulfur Dication Equivalent

We report a one-pot, three-component synthesis of sulfides by exploiting a sulfoxide reagent as a formal sulfur dication equivalent. Our protocol consists of three simple chemical operations involving two Grignard reagents and trimethylsilyl chloride (TMSCl) to sequentially form sulfenate anions, sulfenate esters, and sulfides. We demonstrate a wide range of Grignard reagents to be coupled, thereby allowing the modular, thiol-free synthesis of sulfides including dialkenyl and alkenyl-alkynyl sulfides.

Tandem Ene/[4 + 2] Cycloaddition Reaction for the Synthesis of 9-Benzylphenanthrenes from Arynes and α-(Bromomethyl)styrenes

A tandem reaction for the synthesis of phenanthrenes from arynes and α-(bromomethyl)styrenes is reported. The transformation proceeds via an ene reaction of α-(bromomethyl)styrenes with arynes, followed by a [4 + 2] cycloaddition reaction. The reaction generates 9-benzylphenanthrene derivatives in moderate to excellent yields.

Empowering boronic acids as hydroxyl synthons for aryne induced three-component coupling reactions

Boronic acids have become one of the most prevalent classes of reagents in modern organic synthesis, displaying various reactivity profiles via C-B bond cleavage. Herein, we describe the utilization of a readily available boronic acid as an efficient surrogate of hydroxide upon activation via fluoride complexation. The hitherto unknown aryne induced ring-opening reaction of cyclic sulfides and three-component coupling of fluoro-azaarenes are developed to exemplify the application value. Different from metal hydroxides or water, this novel hydroxy source displays mild activation conditions, great functionality tolerance and structural tunability, which shall engender a new synthetic paradigm and in a broad context offer new blueprints for organoboron chemistry. Detailed computational studies also recognize the fluoride activation mode, provide in-depth insights into the unprecedented mechanistic pathway and elucidate the reactivity difference of ArB(OH) x F y complexes, which fully support the experimental data.

Deaminative Arylation and Alkenyaltion of Aliphatic Tertiary Amines with Aryl and Alkenylboronic Acids via Nitrogen Ylides

Transition-metal-catalyzed Suzuki-Miyaura coupling has significantly advanced C-C bond formation and has been well recognized in organic synthesis, pharmaceuticals, materials science and other fields. In this rapid development, cross coupling without transition metal catalyst is a big challenge in this field, and using widely existing tertiary amines as electrophiles to directly couple with boronic acids has great hurdles yet significant application prospects. Herein, we report an efficient and general deaminative arylation and alkenylation of tertiary amines (propargyl amines, allyl amines and 1H-indol-3-yl methane amines) with ary and alkenylboronic acids enabled by difluorocarbene under transition-metal-free conditions. Preliminary mechanism experiments suggest that in situ formed difluoromethyl quaternary amine salt, nitrogen ylide and tetracoordinate boron species are the key intermediates, the subsequent 1,2-metallate shift and protodeboronation complete the new coupling reaction.

Broadly Applicable Ion Pair-Assisted Nucleophilic Substitution of sp3-Carbon Electrophiles with Alkynyltrifluoroborates

Alkynyltrifluoroborate nucleophiles react smoothly with a wide range of sp³-carbon electrophiles, including propargyl methanesulfonates and unactivated alkyl triflates, to give Sonogashira-type products, via a novel ion pair-assisted nucleophilic substitution mechanism. An ion pair-organic complex, investigated using computational chemistry and in situ NMR experiments, may play a crucial role in this reaction.

Effects of the Chalcogenide Identity in N‐Aryl Phenochalcogenazine Photoredox Catalysts

Phenochalcogenazines such as phenoxazines and phenothiazines have been widely employed as photoredox catalysts (PCs) in small molecule and polymer synthesis. However, the effect of the chalcogenide in these catalysts has not been fully investigated. In this work, a series of four phenochalcogenazines is synthesized to understand how the chalcogenide impacts catalyst properties and performance. Increasing the size of the chalcogenide is found to distort the PC structure, ultimately impacting the properties of each PC. For example, larger chalcogenides destabilize the PC radical cation, possibly resulting in catalyst degradation. In addition, PCs with larger chalcogenides experience increased reorganization during electron transfer, leading to slower electron transfer. Ultimately, catalyst performance is evaluated in organocatalyzed atom transfer radical polymerization and a photooxidation reaction for C(sp²)−N coupling. Results from these experiments highlight that a balance of PC properties is most beneficial for catalysis, including a long‐lived excited state, a stable radical cation, and a low reorganization energy.

Pd-Catalyzed Cross-Coupling of Sb-Aryl Stibines with Halogenomethyl Arenes to Give Unsymmetirc Diarylmethanes

Herein, we describe a general method for the synthesis of unsymmetric diarylmethanes from (hetero)aryl methyl halides and Sb-aryl stibines. This protocol shows a broad substrate scope and a good functional group tolerance. Drug molecules, including beclobrate 3al and bifemelane 3as, and drug derivatives, including celecoxib 3p, ibuprofen 3ao, and probenecid 3ap, were efficiently synthesized on a gram scale. The possible mechanism is proposed on the basis of the results of control experiments.

Origin of Ligand Effects on Stereoinversion in Pd-Catalyzed Synthesis of Tetrasubstituted Olefins

The mechanism and origin of ligand effects on stereoinversion of Pd-catalyzed synthesis of tetrasubstituted olefins were investigated using DFT calculations and the approach of energy decomposition analysis (EDA). The results reveal that the stereoselectivity-determining steps are different when employing different phosphine ligands. This is mainly due to the steric properties of ligands. With the bulkier Xantphos ligand, the syn/anti-to-Pd 1,2-migrations determine the stereoselectivity. While using the less hindered P(o-tol)₃ ligand, the 1,3-migration is the stereoselectivity-determining step. The EDA results demonstrate that Pauli repulsion and polarization are the dominant factors for controlling the stereochemistry in 1,2- and 1,3-migrations, respectively. The origins of differences of Pauli repulsion and polarization between the two stereoselective transition states are further identified.

Regioselective Cross-Coupling of Isatogens with Boronic Acids to Construct 2,2-Disubstituted Indolin-3-one Derivatives

Herein we present a transition-metal-free cross-coupling reaction of isatogens with boronic acids through a 1,4-metalate shift of a boron "ate" complex. This coupling reaction provides a feasible method to deliver valuable 2,2-disubstituted indolin-3-one derivatives with excellent regioselectivity, which exhibit operational simplicity, good functional group tolerance, and a broad substrate scope.

Sulfur-Mediated Reactions through Sulfonium Salts and Ylides

This Account discusses several new reaction methods developed in our group that utilize sulfur-mediated reactions through sulfonium salts and ylides, highlighting the interplay of rational design and serendipity. Our initial goal was to convert aliphatic C–H bonds into C–C bonds site-selectively, and without the use of transition-metal catalysts. While a proof-of-concept has been achieved, this target is far from being ideally realized. The unexpected discovery of an anti-Markovnikov rearrangement and subsequent studies on difunctionalization of alkynes were much more straightforward, and eventually led to the new possibility of asymmetric N–H insertion of sulfonium ylides through Brønsted acid catalysis.

1 Introduction

2 Allylic/Propargylic C–H Functionalization

3 Anti-Markovnikov Rearrangement

4 Difunctionalization of Alkynes

5 Asymmetric N–H Insertion of Sulfonium Ylides

6 Conclusion

Computational study of silver-catalyzed stereoselective hydroalkylation of alkynes: Pauli repulsion controlled Z/E selectivity

The mechanism and origin of stereoselectivity of silver-catalyzed hydroalkylation of alkynes were computationally investigated at the B3LYP-D3BJ/6-311+G(d,p)-SDD//B3LYP/6-31G(d)-LANL2DZ level. The complex of alkynyl trialkylboronate with cationic silver is a key intermediate, which triggers the rate- and stereoselectivity-determining 1,2-migration step. Energy decomposition analysis indicates that the difference of Pauli repulsion dominates the stereoselectivity.

Phosphine-Catalyzed Cross-Coupling of Benzyl Halides and Fumarates

A phosphine-catalyzed olefinic cross-coupling between benzyl halides and fumarates is described, which affords trisubstituted alkenes in good yields and excellent E-selectivity under metal-free conditions. Mechanistic studies suggest a catalytic cycle involving phosphorus ylide formation, Michael addition, water-assisted hydrogen transfer, and phosphine elimination.

Transition-Metal-Free Synthesis of N-Arylphenothiazines through an N- and S-Arylation Sequence

An efficient synthetic method of N-arylphenothiazines from o-sulfanylanilines under transition-metal-free conditions is disclosed. An N- and S-arylation sequence of o-sulfanylanilines enabled us to synthesize a wide variety of N-arylphenothiazines. In particular, one-pot synthesis of N-arylphenothiazines was accomplished from easily available modules through preparation of o-sulfanylanilines by thioamination of aryne intermediates and following N- and S-arylation sequence.

Rhodium-Catalyzed C4-Selective C-H Alkenylation of 2-Pyridones by Traceless Directing Group Strategy

A rhodium-catalyzed C4-selective C-H alkenylation of 3-carboxy-2-pyridones with styrenes has been developed. The carboxylic group at the C3 position works as the traceless directing group, and the corresponding C4-alkenylated 2-pyridones are obtained exclusively with concomitant decarboxylation. Unlike the reported procedures, the exclusive C4 selectivity is uniformly observed even in the presence of potentially more reactive C-H bonds at the C5 and C6 positions. By using this strategy, the multiply substituted 2-pyridone can be prepared via sequential C-H functionalization reactions.

Electrophotocatalytic diamination of vicinal C-H bonds

The conversion of unactivated carbon-hydrogen (C-H) bonds to carbon-nitrogen (C-N) bonds is a highly valued transformation. Existing strategies typically accomplish such reactions at only a single C-H site because the first derivatization diminishes the reactivity of surrounding C-H bonds. Here, we show that alkylated arenes can undergo vicinal C-H diamination reactions to form 1,2-diamine derivatives through an electrophotocatalytic strategy, using acetonitrile as both solvent and nitrogen source. The reaction is catalyzed by a trisaminocyclopropenium (TAC) ion, which undergoes anodic oxidation to furnish a stable radical dication while the cathodic reaction reduces protons to molecular hydrogen. Irradiation of the TAC radical dication (wavelength of maximum absorption of 450 to 550 nanometers) with a white-light compact fluorescent light generates a strongly oxidizing photoexcited intermediate. Depending on the electrolyte used, either 3,4-dihydroimidazole or aziridine products are obtained.

Passerini-type reaction of boronic acids enables α-hydroxyketones synthesis

Multicomponent reactions (MCRs) facilitate the rapid and diverse construction of molecular scaffolds with modularity and step economy. In this work, engagement of boronic acids as carbon nucleophiles culminates in a Passerini-type three-component coupling reaction towards the synthesis of an expanded inventory of α-hydroxyketones with skeletal diversity. In addition to the appealing features of MCRs, this protocol portrays good functional group tolerance, broad substrate scope under mild conditions and operational simplicity. The utility of this chemistry is further demonstrated by amenable modifications of bioactive products and pharmaceuticals as well as in the functionalization of products to useful compounds.

Multicomponent reactions enable the rapid construction of diverse molecular scaffolds with modularity and step economy. In this work, the authors report the use of boronic acids as carbon nucleophiles in a Passerini-type three-component coupling reaction towards an expanded inventory of α-hydroxyketones.

Two Schiff-base Complexes of Copper and Zirconium Oxide Fabricated on Magnetic Nanoparticles as Practical and Recyclable Catalysts in C-C Coupling Reaction

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Fe3O4 magnetic nanoparticles (MNPs) were prepared via a chemical co-precipitation method. Then, the surface of Fe3O4 MNPs was modified by (3-Chloropropyl)trimethoxysilane and then two Schiff-base complexes of zirconium oxide and copper were stabilized on modified Fe3O4 MNPs. These catalysts were characterized using SEM, EDS, WDX, FTIR, XRD, TGA, VSM and AAS techniques. The catalytic activity of these catalysts was described in the carbon-carbon coupling reaction. VSM analysis of these catalysts indicate the high magnetic performance, therefor these catalysts can be recovered by an external magnet and reused for several times without missing in the amount of catalysts. Reusability, excellent yields and high TON values indicate the high efficiency of these catalysts. Leaching of these catalysts was studied by AAS which leaching of copper or zirconium was not observed. Also, the stability of these catalysts was confirmed by characterization of recovered catalysts and comparing with fresh catalysts.

Electrochemical Synthesis of Biaryls via Oxidative Intramolecular Coupling of Tetra(hetero)arylborates

We report herein versatile, transition metal-free and additive-free (hetero)aryl-aryl coupling reactions promoted by the oxidative electrocoupling of unsymmetrical tetra(hetero)arylborates (TABs) prepared from ligand-exchange reactions on potassium trifluoroarylborates. Exploiting the power of electrochemical oxidations, this method complements the existing organoboron toolbox. We demonstrate the broad scope, scalability, and robustness of this unconventional catalyst-free transformation, leading to functionalized biaryls and ultimately furnishing drug-like small molecules, as well as late stage derivatization of natural compounds. In addition, the observed selectivity of the oxidative coupling reaction is related to the electronic structure of the TABs through quantum-chemical calculations and experimental investigations.

Diastereoselective synthesis of spiro-cyclopropanyl-cyclohexadienones via direct sulfide-catalyzed [2 + 1] annulation of para-quinone methides with bromides

A sulfide-catalyzed [2 + 1] annulation of para-quinone methides with diverse bromides was disclosed to access appealing spiro-cyclopropanyl-cyclohexadienones with high diastereoselectivity.

Rh-Catalyzed Highly Enantioselective Synthesis of Aliphatic Sulfonyl Fluorides

Rh-catalyzed, highly enantioselective (up to 99.8% ee) synthesis of aliphatic sulfonyl fluorides was accomplished. This protocol provides a portal to a class of novel 2-aryl substituted chiral sulfonyl fluorides, which are otherwise extremely difficult to access. This asymmetric synthesis has the feature of mild conditions, excellent functional group compatibility, and wide substrate scope (51 examples) generating a wide array of structurally unique chiral β-arylated sulfonyl fluorides for sulfur(VI) fluoride exchange (SuFEx) click reaction and drug discovery.

Sulfur-Mediated Allylic C-H Arylation, Epoxidation, and Aziridination

Transition-metal-free, sulfur-mediated allylic C-H arylation, epoxidation, and aziridination were realized through one-pot procedures. The reaction design involved initial addition between olefins and triflic anhydride activated sulfoxides, followed by subsequent reactions of the allylic sulfur ylides generated under basic conditions with arylboronic acids, aldehydes, or aldimines, to give allylic arylation, epoxidation, or aziridination products, respectively.

Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides, Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts

Organosulfur compounds have long played a vital role in organic chemistry and in the development of novel chemical structures and architectures. Prominent among these organosulfur compounds are those involving a sulfur(IV) center, which have been the subject of countless investigations over more than a hundred years. In addition to a long list of textbook sulfur-based reactions, there has been a sustained interest in the chemistry of organosulfur(IV) compounds in recent years. Of particular interest within organosulfur chemistry is the ease with which the synthetic chemist can effect a wide range of transformations through either bond formation or bond cleavage at sulfur. This review aims to cover the developments of the past decade in the chemistry of organic sulfur(IV) molecules and provide insight into both the wide range of reactions which critically rely on this versatile element and the diverse scaffolds that can thereby be synthesized.

Reactions of organoboron compounds enabled by catalyst-promoted metalate shifts

This tutorial review describes recent developments in catalytic reaction design that involve catalyst-promoted 1,2-metalate shifts as a critical part of the reaction mechanism. Issues pertaining to catalysis, stereoselectivity, and reaction mechanism are discussed.

Transition-Metal-Free Aryl-Aryl Cross-Coupling: C-H Arylation of 2-Naphthols with Diaryliodonium Salts

Transition-metal-free regioselecitive C-H arylation of 2-naphthols with diaryliodonium salts has been developed. The reaction proceeds under very simple experimental conditions and affords a range of products with various substitution patterns. The method allows for the incorporation of electron-deficient aryls, which complements well currently existing metal-free aryl-aryl cross-couplings of phenols that have been so far restricted to the introduction of electron-rich aryl moieties. The mechanism of the reaction was studied by means of DFT calculations, demonstrating that the C-C bond formation occurs via a dearomatization of 2-naphthol substrate, followed by a subsequent rearomatization by tautomerization. The computations show that the use of a low polarity solvent and an insoluble inorganic base is key to securing the high selectivity of the C-C coupling over a competing C-O arylation pathway, by preventing the incipient deprotonation of 2-naphthol.

An Olefinic 1,2-Boryl-Migration Enabled by Radical Addition: Construction of gem-Bis(boryl)alkanes

A series of in situ formed alkenyl diboronate complexes from alkenyl Grignard reagents (commercially available or prepared from alkenyl bromides and Mg) with B₂ Pin₂ (bis(pinacolato)diboron) react with diverse alkyl halides by a Ru photocatalyst to give various gem-bis(boryl)alkanes. Alkyl radicals add efficiently to the alkenyl diboronate complexes, and the adduct radical anions undergo radical-polar crossover, specifically, a 1,2-boryl-anion shift from boron to the α-carbon sp² center. This transformation shows good functional-group compatibility and can serve as a powerful synthetic tool for late-stage functionalization in complex compounds. Measurements of the quantum yield reveal that a radical-chain mechanism is operative in which the alkenyl diboronates acts as reductive quencher for the excited state of the photocatalyst.

Transition-Metal-Free Deconstructive Lactamization of Piperidines

One of the major challenges in organic synthesis is the activation or deconstructive functionalization of unreactive C(sp³ )-C(sp³ ) bonds, which requires using transition or precious metal catalysts. We present here an alternative: the deconstructive lactamization of piperidines without using transition metal catalysts. To this end, we use 3-alkoxyamino-2-piperidones, which were prepared from piperidines through a dual C(sp³ )-H oxidation, as transitory intermediates. Experimental and theoretical studies confirm that this unprecedented lactamization occurs in a tandem manner involving an oxidative deamination of 3-alkoxyamino-2-piperidones to 3-keto-2-piperidones, followed by a regioselective Baeyer-Villiger oxidation to give N-carboxyanhydride intermediates, which finally undergo a spontaneous and concerted decarboxylative intramolecular translactamization.