Nonsymmetrical Bis-Azine Biaryls from Chloroazines: A Strategy Using Phosphorus Ligand-Coupling

De Novo Synthesis of 2,2'-Bipyridines and Related Bis-azines via Cascade Coupling and Double Pyridannulation of Isocyanides

Herein, we present a new and general protocol for the assembly of 2,2'-bipyridyls from nonpyridine substrates without using any metal catalysts or organometallic reagents. The process starts from the coupling of two 1,3-dienyl isocyanides followed by a 6π-electrocyclization/aromatization cascade featuring the simultaneous formation of two pyridine rings in a single operation. Notably, this strategy is also applicable to the construction of nonsymmetrical 2-(2-pyridyl)-quinolines/-quinoxalines. Furthermore, the aggregation-induced emission (AIE) characteristics endow our approach with great potential in biorelevant fields.

Asymmetric Carbene-Alkyne Metathesis-Mediated Cascade: Synthesis of Benzoxazine Polychiral Polyheterocycles and Discovery of a Novel Pain Blocker

This study introduces a novel approach for synthesizing Benzoxazine-centered Polychiral Polyheterocycles (BPCPHCs) via an innovative asymmetric carbene-alkyne metathesis-triggered cascade. Overcoming challenges associated with intricate stereochemistry and multiple chiral centers, the catalytic asymmetric Carbene Alkyne Metathesis-mediated Cascade (CAMC) is employed using dirhodium catalyst/Brønsted acid co-catalysis, ensuring precise stereo control as validated by X-ray crystallography. Systematic substrate scope evaluation establishes exceptional diastereo- and enantioselectivities, creating a unique library of BPCPHCs. Pharmacological exploration identifies twelve BPCPHCs as potent Nav ion channel blockers, notably compound 8 g. In vivo studies demonstrate that intrathecal injection of 8 g effectively reverses mechanical hyperalgesia associated with chemotherapy-induced peripheral neuropathy (CIPN), suggesting a promising therapeutic avenue. Electrophysiological investigations unveil the inhibitory effects of 8 g on Nav1.7 currents. Molecular docking, dynamics simulations and surface plasmon resonance (SPR) assay provide insights into the stable complex formation and favorable binding free energy of 8 g with C5aR1. This research represents a significant advancement in asymmetric CAMC for BPCPHCs and unveils BPCPHC 8 g as a promising, uniquely acting pain blocker, establishing a C5aR1-Nav1.7 connection in the context of CIPN.

N-Heteroaromatic Fluoroalkylation through Ligand Coupling Reaction of Sulfones

Ligand coupling on hypervalent main group elements has emerged as a pivotal methodology for the synthesis of functionalized N-heteroaromatic compounds in recent years due to the avoidance of transition metals and the mildness of the reaction conditions. In this direction, the reaction of N-heteroaryl sulfur(IV) and N-heteroaryl phosphorus(V) compounds has been well studied. However, the ligand coupling of sulfur(VI) is still underdeveloped and the reaction of alkyl N-heteroarylsulfones is still elusive, which does not match the high status of sulfones as the chemical chameleons in organic synthesis. Here we present a ligand coupling-enabled formal SO2 extrusion of fluoroalkyl 2-azaheteroarylsulfones under the promotion of Grignard reagents, which not only enriches the chemistry of sulfones, but also provides a novel and practical synthetic tool towards N-heteroaromatic fluoroalkylation.

Cathodically Coupled Electrolysis to Access Biheteroaryls

An electrochemical approach to biheteroaryls through the coupling of diverse N-heteroarenes with heteroaryl phosphonium salts is reported. The reaction features pH and redox-neutral conditions and excellent regioselectivity, as well as exogenous air or moisture tolerance. Additionally, a one-pot, two-step protocol can be established to realize formal C-H/C-H coupling of heteroarenes, thereby greatly expanding the substrate availability. The utility of this method is demonstrated through late-stage functionalization, the total synthesis of nitraridine, and antifungal activity studies.

Recent Progress on the Synthesis of Bipyridine Derivatives

Bipyridine and related compounds are starting materials or precursors for a variety of valuable substances such as biologically active molecules, ligands for catalysts, photosensitizers, viologens, and supramolecular architectures. Thus, it is important to classify their synthesis methods and understand their characteristics. Representative examples include methods using homo and heterocoupling of pyridine derivatives in the presence of a catalyst. Because bipyridine compounds strongly coordinate with metal centers, a decrease in catalytic activity and yield is often observed in the reaction system. To address this issue, this review provides insights into advances over the last ~30 years in bipyridine synthesis using metal complexes under both homogeneous and heterogeneous conditions. Moreover, strategies for bipyridine synthesis involving sulfur and phosphorous compounds are examined. These alternative pathways offer promising avenues for overcoming the challenges associated with traditional catalysis methods, providing a more comprehensive understanding of the synthesis landscape.

Data science enabled discovery of a highly soluble 2,2'-bipyrimidine anolyte for application in a flow battery

Development of non-aqueous redox flow batteries as a viable energy storage solution relies upon the identification of soluble charge carriers capable of storing large amounts of energy over extended time periods. A combination of metrics including number of electrons stored per molecule, redox potential, stability, and solubility of the charge carrier impact performance. In this context, we recently reported a 2,2'-bipyrimidine charge carrier that stores two electrons per molecule with reduction near -2.0 V vs. Fc/Fc+ and high stability. However, these first-generation derivatives showed a modest solubility of 0.17 M (0.34 M e-). Seeking to improve solubility without sacrificing stability, we harnessed the synthetic modularity of this scaffold to design a library of sixteen candidates. Using computed molecular descriptors and a single node decision tree, we found that minimization of the solvent accessible surface area (SASA) can be used to predict derivatives with enhanced solubility. This parameter was used in combination with a heatmap describing stability to de-risk a virtual screen that ultimately identified a 2,2'-bipyrimidine with significantly increased solubility and good stability metrics in the reduced states. This molecule was paired with a cyclopropenium catholyte in a prototype all-organic redox flow battery, achieving a cell potential up to 3 V.

Electrochemical synthesis of biaryls by reductive extrusion from N,N'-diarylureas

The synthesis of biaryl compounds by the transition-metal free coupling of arenes is an important contemporary challenge, aiming to avoid the toxicity and cost profiles associated with the metal catalysts commonly used in the synthesis of these pharmaceutically relevant motifs. In this paper, we describe an electrochemical approach to the synthesis of biaryls in which aniline derivatives are coupled through the formation and reduction of a temporary urea linkage. The conformational alignment of the arenes in the N,N'-diaryl urea intermediates promotes C-C bond formation following single-electron reduction. Our optimized conditions are suitable for the synthesis of a variety of biaryls, including sterically hindered examples carrying ortho-substituents, representing complementary reactivity to most metal catalysed methods.

P(III)-Promoted Reductive Coupling of Aromatic and Aliphatic Nitro Compounds with Grignard Reagents

A phosphine-promoted reductive coupling of nitro compounds with Grignard reagents is described. Polyfunctional and pharmaceutically relevant diarylamines were generated by this reaction in moderate to high yields. Aliphatic nitro compounds that are highly challenging substrates undergo a combination of α-arylation and reductive coupling to afford the α-arylated arylamines efficiently. A series of valuable biaryl compounds with polyfluorinated and heteroaryl rings are co-generated in 56-94% yields.

Organophosphine as an Alkyl Transfer Shuttle for the Direct β-Alkylation of Chalcones Using Alkyl Halides

We report an efficient alkyl transfer strategy for the direct β-alkylation of chalcones using commercially available alkyl bromides as alkyl reagents. In this transformation, the ortho-phosphanyl substituent in the chalcones is crucial for controlling their reactivity and selectivity. It also serves as a reliable alkyl transfer shuttle to transform electrophilic alkyl bromides into nucleophilic alkyl species in the form of quaternary phosphonium salts and transfer the alkyl group effectively to the β-position of the chalcones. This alkyl transfer strategy can be further extended to the alkenylation of ortho-phosphanyl benzaldehydes to assemble functionalized polyenes.

Accessing unsymmetrical Ru(II) bipyridine complexes: a versatile synthetic mechanism for fine tuning photophysical properties

Three novel unsymmetrical Ru(II) bipyridine complexes were generated via a convenient, modular, convergent synthetic route. An investigation of their photophysical properties revealed solvent-dependent excited state behaviour including altered absorption and emission wavelengths, emission lifetimes and quantum yields of phosphorescence.

Site-Selective Pyridine C-H Alkylation with Alcohols and Thiols via Single-Electron Transfer of Frustrated Lewis Pairs

A unified strategy for the deoxygenative or desulfurative pyridylation of various alcohols and thiols has been developed through a single-electron transfer (SET) process of frustrated Lewis pairs (FLPs) derived from pyridinium salts and PtBu₃ . Mechanistic studies revealed that N-amidopyridinium salts serve as effective Lewis acids for the formation of FLPs with PtBu₃ , and the generated phosphine radical cation ionically couples with the in situ generated xanthate, eventually affording the alkyl radical through facile β-scission under photocatalyst-free conditions. The reaction efficiency was further accelerated by visible-light irradiation. This method is conceptually appealing by using encounter complexes in FLP chemistry to promote SET, which provides a previously unrecognized opportunity for the selective heteroarylation of a diverse range of alcohols and thiols with various functional groups, even in complex settings under mild reaction conditions.

Metal-Free Phosphination and Continued Functionalization of Pyridine: A Theoretical Study

This study investigates the mechanism of metal-free pyridine phosphination with P(OEt)₃, PPh₃, and PAr₂CF₃ using density functional theory calculations. The results show that the reaction mechanism and rate-determining step vary depending on the phosphine and additive used. For example, phosphination of pyridine with P(OEt)₃ occurs in five stages, and ethyl abstraction is the rate-determining step. Meanwhile, 2-Ph-pyridine phosphination with PPh₃ is a four-step reaction with proton abstraction as the rate-limiting step. Energy decomposition analysis of the transition states reveals that steric hindrance in the phosphine molecule plays a key role in the site-selective formation of the phosphonium salt. The mechanism of 2-Ph-pyridine phosphination with PAr₂CF₃ is similar to that with PPh₃, and analyses of the effects of substituents show that electron-withdrawing groups decreased the nucleophilicity of the phosphine, whereas aryl electron-donating groups increased it. Finally, TfO⁻ plays an important role in the C–H fluoroalkylation of pyridine, as it brings weak interactions.

Palladium-Catalyzed Sonogashira Coupling of a Heterocyclic Phosphonium Salt with a Terminal Alkyne

An efficient Sonogashira coupling of a heterocyclic phosphonium salt with a terminal alkyne via C-P bond cleavage was developed. The reactions proceeded smoothly in the presence of palladium catalyst, copper(I) iodide, and N,N-diisopropylethylamine (DIPEA) in N-methyl-2-pyrrolidone (NMP) at 100 °C for 12 h, producing the corresponding alkynyl-substituted pyridine, quinoline, pyrazine, and quinoxaline in moderate to good yields with wide substrate scope and broad functional group tolerance. In addition, gram-scale synthesis could also be achieved, and the reaction could be applied to the functionalization of alkyne-containing complex molecules derived from sugars and pharmaceutical and naturally occurring products (e.g., estrone, d-galactopyranose, menthol, and ibuprofen).

Relative rates of alkylation for B-substituted triarylphosphines: an ortho-Boron group enhances reactivity on phosphorus

Advancements in main-group catalysis are contingent on our ability to quantify effects that enhance reactivity in these systems. Herein we report the rates of alkylation for several substituted phosphines. We report that by incorporating a single pinacol boronic ester group in the ortho-position on triphenylphosphine, the rate of substitution with benzyl bromide is approximately 4.7 times faster than the parent compound as measured by initial rates. The corresponding meta- and para-isomers are only 1.3 and 1.5 times as fast, respectively. Using X-ray crystallographic data and quantum chemical calculations, we propose this rate acceleration occurs from an O to P electrostatic interaction that stabilizes the transition state.

A General, Multimetallic Cross-Ullmann Biheteroaryl Synthesis from Heteroaryl Halides and Heteroaryl Triflates

Despite their importance to medicine and materials science, the synthesis of biheteroaryls by cross-coupling remains challenging. We describe here a new, general approach to biheteroaryls: the Ni- and Pd-catalyzed multimetallic cross-Ullmann coupling of heteroaryl halides with triflates. An array of 5-membered, 6-membered, and fused heteroaryl bromides and chlorides, as well as aryl triflates derived from heterocyclic phenols, proved to be viable substrates in this reaction (62 examples, 63 ± 17% average yield). The generality of this approach to biheteroaryls was further demonstrated in 96-well plate format at 10 μmol scale. An array of 96 possible products provided >90% hit rate under a single set of conditions. Further, low-yielding combinations could be rapidly optimized with a single "Toolbox Plate" of ligands, additives, and reductants.

Synthesis of Bis-heteroaryls Using Grignard Reagents and Pyridylsulfonium Salts

Herein are reported ligand-coupling reactions of Grignard reagents with pyridylsulfonium salts. The method has wide functional group tolerance and enables the formation of bis-heterocycle linkages, including 2,4′-, 2,3′-, and 2,2′-bipyridines, as well as pyridines linked to pyrimidines, pyrazines, isoxazoles, and benzothiophenes. The methodology was successfully applied to the synthesis of the natural products caerulomycin A and E.

Nickel-Catalyzed Reductive Csp2-Csp3 Cross Coupling Using Phosphonium Salts

A nickel-catalyzed reductive cross coupling with phosphonium salts and allylic C(sp³)-O bond electrophiles, which granted direct construction of the C(sp²)-C(sp³) bond, is successfully developed. The protocol features broad substrate scope, high-functional-group tolerance, and heterocycle compatibility. Notably, the much more challenging reductive cross coupling with heterocyclic thiazolylphosphonium salts has also been accomplished for the first time.

Base-Activated Latent Heteroaromatic Sulfinates as Nucleophilic Coupling Partners in Palladium-Catalyzed Cross-Coupling Reactions

Heteroaromatic sulfinates are effective nucleophilic reagents in Pd0 -catalyzed cross-coupling reactions with aryl halides. However, metal sulfinate salts can be challenging to purify, solubilize in reaction media, and are not tolerant to multi-step transformations. Here we introduce base-activated, latent sulfinate reagents: β-nitrile and β-ester sulfones. We show that under the cross-coupling conditions, these species generate the sulfinate salt in situ, which then undergo efficient palladium-catalyzed desulfinative cross-coupling with (hetero)aryl bromides to deliver a broad range of biaryls. These latent sulfinate reagents have proven to be stable through multi-step substrate elaboration, and amenable to scale-up.

From Pyridine-N-oxides to 2-Functionalized Pyridines through Pyridyl Phosphonium Salts: An Umpolung Strategy

The reactions of pyridine-N-oxides with Ph₃P under the developed conditions provide an unprecedented route to (pyridine-2-yl)phosphonium salts. Upon activation with DABCO, these salts readily serve as functionalized 2-pyridyl nucleophile equivalents. This umpolung strategy allows for the selective C2 functionalization of the pyridine ring with electrophiles, avoiding the generation and use of unstable organometallic reagents. The protocol operates at ambient temperature and tolerates sensitive functional groups, enabling the synthesis of otherwise challenging compounds.

Recent Advances in the Synthesis of 2,2′-Bipyridines and Their Derivatives

The sustained interest in the synthesis of new analogues of 2,2′-bipyridines is supported by the importance of compounds featuring bipyridine core in diverse areas of chemical, biomedical and materials research, which is relayed into the development of new approaches and the expansion of existing synthetic methods. This short review covers advances in the synthesis of 2,2′-bipyridines, including both the synthesis of compounds with a given substitution pattern and the development of new methods for assembling the bipyridine core. Special attention is directed toward the use of pyridine N-oxides and metal-free protocols to facilitate the formation of bipyridines. This short review focuses primarily on reports published in the last 5–6 years.

1 Introduction

2 Ullmann-Type Homocoupling Reactions

3 Cross-Coupling Reactions in the Synthesis of Bipyridines

4 Coupling Reactions Employing Pyridine N-Oxides

5 Other Methods for the Synthesis of 2,2′-Bipyridines

6 Conclusions and Outlook

The 2-Pyridyl Problem: Challenging Nucleophiles in Cross-Coupling Arylations

Azine-containing biaryls are ubiquitous scaffolds in many areas of chemistry, and efficient methods for their synthesis are continually desired. Pyridine rings are prominent amongst these motifs. Transition-metal-catalysed cross-coupling reactions have been widely used for their synthesis and functionalisation as they often provide a swift and tuneable route to related biaryl scaffolds. However, 2-pyridine organometallics are capricious coupling partners and 2-pyridyl boron reagents in particular are notorious for their instability and poor reactivity in Suzuki-Miyaura cross-coupling reactions. The synthesis of pyridine-containing biaryls is therefore limited, and methods for the formation of unsymmetrical 2,2'-bis-pyridines are scarce. This Review focuses on the methods developed for the challenging coupling of 2-pyridine nucleophiles with (hetero)aryl electrophiles, and ranges from traditional cross-coupling processes to alternative nucleophilic reagents and novel main group approaches.

Phosphorus-mediated sp2-sp3 couplings for C-H fluoroalkylation of azines

Fluoroalkyl groups profoundly affect the physical properties of pharmaceuticals and influence almost all metrics associated with their pharmacokinetic and pharmacodynamic profile^1-4. Drug candidates increasingly contain trifluoromethyl (CF₃) and difluoromethyl (CF₂H) groups, and the same trend in agrochemical development shows that the effect of fluoroalkylation translates across human, insect and plant life^5,6. New fluoroalkylation reactions have undoubtedly stimulated this shift; however, methods that directly convert C-H bonds into C-CF₂X groups (where X is F or H) in complex drug-like molecules are rare^7-13. Pyridines are the most common aromatic heterocycles in pharmaceuticals¹⁴, but only one approach-via fluoroalkyl radicals-is viable for achieving pyridyl C-H fluoroalkylation in the elaborate structures encountered during drug development^15-17. Here we develop a set of bench-stable fluoroalkylphosphines that directly convert the C-H bonds in pyridine building blocks, drug-like fragments and pharmaceuticals into fluoroalkyl derivatives. No preinstalled functional groups or directing groups are required. The reaction tolerates a variety of sterically and electronically distinct pyridines, and is exclusively selective for the 4-position in most cases. The reaction proceeds through initial formation of phosphonium salts followed by sp²-sp³ coupling of phosphorus ligands-an underdeveloped manifold for forming C-C bonds.

Phosphorus-Based Catalysis

Phosphorus-based organocatalysis encompasses several subfields that have undergone rapid growth in recent years. This Outlook gives an overview of its various aspects. In particular, we highlight key advances in three topics: nucleophilic phosphine catalysis, organophosphorus catalysis to bypass phosphine oxide waste, and organophosphorus compound-mediated single electron transfer processes. We briefly summarize five additional topics: chiral phosphoric acid catalysis, phosphine oxide Lewis base catalysis, iminophosphorane super base catalysis, phosphonium salt phase transfer catalysis, and frustrated Lewis pair catalysis. Although it is not catalytic in nature, we also discuss novel discoveries that are emerging in phosphorus(V) ligand coupling. We conclude with some ideas about the future of organophosphorus catalysis.

Selective C-H chalcogenation of thiazoles via thiazol-2-yl-phosphonium salts

Thiazoles and benzothiazoles undergo regioselective C2-H chalcogenation via the sequence of thiazole C2-functionalization with phosphines to produce phosphonium salts which in turn react with S- and Se-centered nucleophiles to give products of C2-H chalcogenation and allow for recovery of the starting phosphine. The atom economical sequence proceeds under mild conditions and features broad scope for both the nucleophiles (electron-rich, electron-poor, sterically hindered thiols) and the various substituted benzothiazoles. The access to the substituted medicinally relevant C2-thio benzothiazoles also enables stereoselectivity improvements in the modified Julia olefinations.

Main Group Redox Catalysis of Organopnictogens: Vertical Periodic Trends and Emerging Opportunities in Group 15

A growing number of organopnictogen redox catalytic methods have emerged-especially within the past 10 years-that leverage the plentiful reversible two-electron redox chemistry within Group 15. The goal of this Perspective is to provide readers the context to understand the dramatic developments in organopnictogen catalysis over the past decade with an eye toward future development. An exposition of the fundamental differences in the atomic structure and bonding of the pnictogens, and thus the molecular electronic structure of organopnictogen compounds, is presented to establish the backdrop against which organopnictogen redox reactivity-and ultimately catalysis-is framed. A deep appreciation of these underlying periodic principles informs an understanding of the differing modes of organopnictogen redox catalysis and evokes the key challenges to the field moving forward. We close by addressing forward-looking directions likely to animate this area in the years to come. What new catalytic manifolds can be developed through creative catalyst and reaction design that take advantage of the intrinsic redox reactivity of the pnictogens to drive new discoveries in catalysis?

Nickel-catalyzed direct cross-coupling of heterocyclic phosphonium salts with aryl bromides

The cross-couplings of heterocyclic phosphonium salts with aryl bromides proceeded effectively in the presence of nickel(ii) catalyst, bipyridine ligand, magnesium, and LiCl, providing an easy entry to 4-arylated pyridines, quinolines, and pyrazines.

Facile Pyridine S N Ar Reactions via N-Phosphonium-Pyridinium Intermediates

Here we report that N-phosphonium pyridinium intermediates are unusually reactive for pyridine S N Ar reactions. Specifically, forming phosphonium salts from halopyridines typically requires elevated temperatures and Lewis acid additives. The alternative activation mode described in this paper permits C-P bond formation to occur at ambient temperatures in many cases, and functions across a broad range of substrates.

Z-Selective phosphine promoted 1,4-reduction of ynoates and propynoic amides in the presence of water

Phosphine-mediated reductions of substituted propynoic esters and amides in the presence of water yield the partially reduced α,β-unsaturated esters and amides with high Z-selectivity. The competitive in situ Z to E-isomerization of the product in some cases lowers the Z to E ratios of the isolated α,β-unsaturated carbonyl products. Reaction time and the amounts of phosphine and water in the reaction mixture are the key experimental factors which control the selectivity by preventing or reducing the rates of Z- to E-product isomerization. Close reaction monitoring enables isolation of the Z-alkenes with high selectivities. The computational results suggest that the reactions could be highly Z-selective owing to the stereoselective formation of the E-P-hydroxyphosphorane intermediate.

Recent Developments in Transition-Metal-Free Functionalization and Derivatization Reactions of Pyridines

Pyridine is an important structural motif that is prevalent in natural products, drugs, and materials. Methods that functionalize and derivatize pyridines have gained significant attention. Recently, a large number of transition-metal-free reactions have been developed. In this review, we provide a brief summary of recent advances in transition-metal-free functionalization and derivatization reactions of pyridines, categorized according to their reaction modes.

1 Introduction

2 Metalated Pyridines as Nucleophiles

2.1 Deprotonation

2.2 Halogen–Metal exchange

3 Activated Pyridines as Electrophiles

3.1 Asymmetric 2-Allylation by Chiral Phosphite Catalysis

3.2 Activation of Pyridines by a Bifunctional Activating Group

3.3 Alkylation of Pyridines by 1,2-Migration

3.4 Alkylation of Pyridines by [3+2] Addition

3.5 Pyridine Derivatization by Catalytic In Situ Activation Strategies

3.6 Reactions via Heterocyclic Phosphonium Salts

4 Radical Reactions for Pyridine Functionalization

4.1 Pyridine Functionalization through Radical Addition Reactions

4.2 Pyridine Functionalization through Radical–Radical Coupling Reactions

5 Derivatization of Pyridines through the Formation of Meisenheimer-Type Pyridyl Anions

6 Conclusion

Synthesis of Pyridylsulfonium Salts and Their Application in the Formation of Functionalized Bipyridines

An S-selective arylation of pyridylsulfides with good functional group tolerance was developed. To demonstrate synthetic utility, the resulting pyridylsulfonium salts were used in a scalable transition-metal-free coupling protocol, yielding functionalized bipyridines with extensive functional group tolerance. This modular methodology permits selective introduction of functional groups from commercially available pyridyl halides, furnishing symmetrical and unsymmetrical 2,2'- and 2,3'-bipyridines. Iterative application of the methodology enabled the synthesis of a functionalized terpyridine with three different pyridine components.

Late stage C-H functionalization via chalcogen and pnictogen salts

Late-stage functionalization (LSF) of heteroarenes can dramatically accelerate SAR studies by enabling the installation of functional groups that would otherwise complicate a synthetic sequence. Although heteroaryl halides and boronic esters have well-established chemistries for LSF, alternatives that enable site-selective C-H functionalization are highly attractive. Recently, three unrelated cationic groups (phosphonium, pyridinium, and thianthrenium), which can replace C-H bonds late stage, have been identified as precursors to various functional groups. This review will discuss the synthesis and application of these three salts with an emphasis on their use for LSF and application to medicinal chemistry.

Palladium-Catalyzed Electrophilic Functionalization of Pyridine Derivatives through Phosphonium Salts

Herein, we report a highly efficient and practical method for pyridine-derived heterobiaryl synthesis through palladium-catalyzed electrophilic functionalization of easily available pyridine-derived quaternary phosphonium salts. The nice generality of this reaction was goes beyond arylation, enabling facile incorporation of diverse carbon-based fragments, including alkenyl, alkynyl, and also allyl fragments, onto the pyridine core. Notably, the silver salt additive is revealed to be of vital importance for the success of this transformation and its pivotal role as transmetallation mediator, which guarantees a smooth transfer of pyridyl group to palladium intermediate, is also described.

Sulfur(IV)-Mediated Unsymmetrical Heterocycle Cross-Couplings

Despite the tremendous utilities of metal-mediated cross-couplings in modern organic chemistry, coupling reactions involving nitrogenous heteroarenes remain a challenging undertaking - coordination of Lewis basic atoms into metal centers often necessitate elevated temperature, high catalyst loading, etc. Herein, we report a sulfur (IV) mediated cross-coupling amendable for the efficient synthesis of heteroaromatic substrates. Addition of heteroaryl nucleophiles to a simple, readily-accessible alkyl sulfinyl (IV) chloride allows formation of a trigonal bipyramidal sulfurane intermediate. Reductive elimination therefrom provides bis-heteroaryl products in a practical and efficient fashion.