A general and efficient method for the Suzuki-Miyaura coupling of 2-pyridyl nucleophiles

General room-temperature Suzuki-Miyaura polymerization for organic electronics

π-Conjugated polymers (CPs) have broad applications in high-performance optoelectronics, energy storage, sensors and biomedicine. However, developing green and efficient methods to precisely synthesize alternating CP structures on a large scale remains challenging and critical for their industrialization. Here a room-temperature, scalable and homogeneous Suzuki-Miyaura-type polymerization reaction is developed with broad generality validated for 24 CPs including donor-donor, donor-acceptor and acceptor-acceptor connectivities, yielding device-quality polymers with high molecular masses. Furthermore, the polymerization protocol significantly reduces homocoupling structural defects, yielding more structurally regular and higher-performance electronic materials and optoelectronic devices than conventional thermally activated polymerizations. Experimental and theoretical studies reveal that a borate transmetalation process plays a key role in suppressing protodeboronation, which is critical for large-scale structural regularity. Thus, these results provide a general polymerization tool for the scalable production of device-quality CPs with alternating structural regularity.

Oxazaborolidinones: Steric Coverage Effect of Lewis Acidic Boron Center in Suzuki-Miyaura Coupling Reactions

It was demonstrated that α-hydroxycarboxamide is an excellent boron-protecting group. The reaction between α-hydroxycarboxamide and organoboronic acids produced stable oxazaborolidinones (OxBs), in which thesp 2 ${{_{{\rm sp}{^{2}}}}}$ -hybridized boron atom was sterically protected by α-hydroxycarboxamide. The alkyl groups of the α-hydroxycarboxamide moiety can dynamically cover the p-orbital of thesp 2 ${{_{{\rm sp}{^{2}}}}}$ -hybridized boron center, creating a small space around the boron atom, allowing for smooth transmetalation by a Pd catalyst and easy deprotection by water. This protecting phenomenon is effective for readily purification, Suzuki-Miyaura coupling reactions with unstable boronic acids and iterative cross-couplings.

A Multi-Objective Active Learning Platform and Web App for Reaction Optimization

We report the development of an open-source experimental design via Bayesian optimization platform for multi-objective reaction optimization. Using high-throughput experimentation (HTE) and virtual screening data sets containing high-dimensional continuous and discrete variables, we optimized the performance of the platform by fine-tuning the algorithm components such as reaction encodings, surrogate model parameters, and initialization techniques. Having established the framework, we applied the optimizer to real-world test scenarios for the simultaneous optimization of the reaction yield and enantioselectivity in a Ni/photoredox-catalyzed enantioselective cross-electrophile coupling of styrene oxide with two different aryl iodide substrates. Starting with no previous experimental data, the Bayesian optimizer identified reaction conditions that surpassed the previously human-driven optimization campaigns within 15 and 24 experiments, for each substrate, among 1728 possible configurations available in each optimization. To make the platform more accessible to nonexperts, we developed a graphical user interface (GUI) that can be accessed online through a web-based application and incorporated features such as condition modification on the fly and data visualization. This web application does not require software installation, removing any programming barrier to use the platform, which enables chemists to integrate Bayesian optimization routines into their everyday laboratory practices.

Chemodivergent Organolanthanide-Catalyzed C-H α-Mono-Borylation of Pyridines

Chemodivergent synthetic methodologies enable the efficient introduction of structural diversity into high-value organic products via simple chemical alterations. In this regard, C-H activation and functionalization of pyridinoid azines are important transformations in the synthesis of many natural products, pharmaceuticals, and functional materials. Reflecting on azinyl nitrogen lone-pair steric repulsion, its tendency to irreversibly coordinate metal ion catalysts, and the electron deficiency of pyridine, C-H functionalization at the important α-position remains challenging. Thus, developing earth-abundant catalysts for α-selective azine mono-functionalization is an attractive target for chemical synthesis. Here, the selective organolanthanide-catalyzed α-mono-borylation of a diverse series of 18 pyridines is reported using Cp*₂LuCH(TMS)₂ (Cp* = η⁵-C₅Me₅) (TMS = SiMe₃) and affording valuable precursors for subsequent functionalization. Experimental and theoretical mechanistic data reported here support the intermediacy of a C-H-activated η²-lanthanide-azine complex, followed by intermolecular α-mono-borylation via σ-bond metathesis. Notably, varying the lanthanide identity and substrate substituent electronic character promotes marked chemodivergence of the catalytic selectivity: smaller/more electrophilic lanthanide³⁺ ions and electron-rich substrates favor selective α-C-H functionalization, whereas larger/less electrophilic lanthanide³⁺ ions and electron-poor substrates favor selective B-N bond-forming 1,2-dearomatization. Such lanthanide series catalytic chemodivergence is, to our knowledge, unprecedented.

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.

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.

Heteroaryl-Heteroaryl, Suzuki-Miyaura, Anhydrous Cross-Coupling Reactions Enabled by Trimethyl Borate

Reaction conditions have been developed for refractory heteroaryl-heteroaryl Suzuki-Miyaura cross-couplings. The reported method employs neopentyl heteroarylboronic esters as nucleophiles, heteroaryl bromides and chlorides as the electrophiles, and the soluble base potassium trimethylsilanolate (TMSOK) under anhydrous conditions. The addition of trimethyl borate enhances reaction rates by several mechanisms, including (1) solubilization of in situ-generated boronate complexes, (2) preventing catalyst poisoning by the heteroatomic units, and (3) buffering the inhibitory effect of excess TMSOK. The use of this method enables cross-coupling of diverse reaction partners including a broad range of π-rich and π-deficient heteroaryl boronic esters and heteroaryl bromides. Reactions proceed in good yields and short reaction times (3 h or less).

Divergent reactivities of 2-pyridyl sulfonate esters. Exceptionally mild access to alkyl bromides and 2-substituted pyridines

A series of 2- and 3-pyridyl sulfonate and tosylate esters of primary and secondary alcohols were synthesized and evaluated in the bromination reaction with MgBr2·Et2O. The greater coordinating ability of the 2-pyridyl sulfonate esters accounted for its observed superior reactivity and selectivity. Reaction of neopentyl and phenyl 2-pyridyl sulfonates with a variety of aryl and heteroaryl Li reagents led to 2-substituted pyridines at temperatures as low as −78 °C via an SNAr process. Mechanistic considerations are discussed.

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.

Cyrene™ as a Neoteric Bio-Based Solvent for Catalyst-Free Microwave-Assisted Construction of Diverse Bipyridine Analogues for Heavy-Metal Sensing

An environment-friendly synthetic protocol was developed to access polyfunctionalized bipyridines from readily available amines, chromone-3-carboxaldehydes, and pyridinylacetonitriles under catalyst- and additive-free conditions using the bio-renewable neoteric solvent dihydrolevoglucosenone (Cyrene™). In this strategy, amines served as both a mild-base promoter and a substrate. In addition, water was the only by-product of this reaction. This multi-component protocol provided highly diverse 2,3-, 3,3-, and 3,4-bipyridines in good-to-excellent yields. Operational simplicity, short reaction time, excellent atom economy, and easily obtainable substrates are among the features of this microwave-assisted synthesis. Additionally, the compounds synthesized via this method have demonstrated the ability to detect heavy metals, specifically mercury(II), copper(II), and iron (III) ions.

Cross-Coupled Phenyl- and Alkynyl-Based Phenanthrolines and Their Effect on the Photophysical and Electrochemical Properties of Heteroleptic Cu(I) Photosensitizers

With the aims of increasing the antenna system and improving the photophysical properties of Cu(I)-based photosensitizers, the backbone of 2,9-dimethyl-1,10-phenanthroline was selectively extended in the 5,6-position. Applying specifically tailored Suzuki-Miyaura and "chemistry-on-the-complex" Sonogashira cross-coupling reactions enabled the development of two sets of structurally related diimine ligands with a broad variety of different phenyl- and alkynyl-based substituents. The resulting 11 novel heteroleptic Cu(I) complexes, including five solid-state structures, were studied with respect to their structure-property relationships. Both sets of substituents are able to red-shift the absorption maxima and to increase the absorptivity. For the alkynyl-based complexes, this is accompanied by a significant anodic shift of the reduction potentials. The phenyl-based substituents strongly influence the emission wavelength and quantum yield of the resulting Cu(I) complexes and lead to an increase in the emission lifetime of up to 504 ns, which clearly indicates competition with the benchmark system [(xantphos)Cu(bathocuproine)]PF₆.

Highly chemoselective deoxygenation of N-heterocyclic N-oxides under transition metal-free conditions

Because their site-selective C-H functionalizations are now considered one of the most useful tools for synthesizing various N-heterocyclic compounds, the highly chemoselective deoxygenation of densely functionalized N-heterocyclic N-oxides has received much attention from the synthetic chemistry community. Here, we provide a protocol for the highly chemoselective deoxygenation of various functionalized N-oxides under visible light-mediated photoredox conditions with Na2-eosin Y as an organophotocatalyst. Mechanistic studies imply that the excited state of the organophotocatalyst is reductively quenched by Hantzsch esters. This operationally simple technique tolerates a wide range of functional groups and allows high-yield, multigram-scale deoxygenation.

A four-coordinate Cu(I)–N-heterocyclic carbene complex: Synthesis, structure, properties, and application in amination for the synthesis of 1-(2-N-heteroaryl)-1H-pyrazoles

A new luminescent, cationic, heteroleptic, four-coordinate Cu(I)– N-heterocyclic carbene complex [Cu(Br-Pyim)(POP)](PF6) is successfully prepared and characterized, where Br-Pyim and POP are 1-(6-bromopyridin-2-yl)imidazole-3-benzyl-2-ylidene and bis[2-(diphenylphosphino)phenyl]ether, respectively. Its detailed structure is determined by single-crystal X-ray analysis. It exists as a crystalline powder at room temperature and exhibits bright yellow-green emission. The use of the Cu(I)– N-heterocyclic carbene complex as a catalyst for amination reactions is also investigated and is found to be very efficient for the amination of 2- N-heteroaryl chlorides with pyrazoles, giving the desired substituted 1-(2- N-heteroaryl)-1 H-pyrazoles in good yields.

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.

Perylenequinonoid-catalyzed photoredox activation for the direct arylation of (het)arenes with sunlight

Naturally occurring perylenequinonoid pigments (PQPs) have attracted considerable attention owing to their excellent properties of photosensitization. They have been widely investigated as an aspect of photophysics and photobiology. However, their applications in photocatalysis are yet to be explored. We report here that sunlight along with 1 mol% cercosporin, which is one of the perylenequinonoid pigments, catalyzes the direct C-H bond arylation of (het)arenes by a photoredox process with good regioselectivity and broad functional group compatibility. Furthermore, a gram-scale reaction with great conversions of substrates was achieved even by a cercosporin-containing supernatant without organic solvent extraction and purification after liquid fermentation. Thus we set up a bridge between microbial fermentation and organic photocatalysis for chemical reactions in a sustainable, environmentally friendly manner.

Single-Pot Access to Bisorganoborinates: Applications in Zweifel Olefination

Zweifel olefination is a catalyst-free reaction that serves alkene functionalization. While most methods employ commercially available boron pinacol esters, we have assembled a sequence in which the two partners of the formal coupling reaction are installed successively, starting from inexpensive boron alkoxides. The in situ formation of bisorganoborinates was accomplished by consecutive reaction of two different organometallic species. This single-pot procedure represents a great advancement in the generation of organoborinates and their involvement in C-C bond formation.

Coordination chemistry and catalysis with secondary phosphine oxides

Review on synthesis, coordination chemistry and catalysis with secondary phosphine oxides.

Cu-Catalysed carboxylation of aryl boronic acids with CO2

A copper/N-heterocyclic carbene (NHC) catalysed carboxylation of aryl boronic acids under one atmospheric pressure of CO₂ has been developed.

Zinc phthalocyanine activated by conventional indoor light makes a highly efficient antimicrobial material from regular cellulose

A phthalocyanine-cellulose material quickly inactivates drug-resistant microbes under indoor light.

Crystal structure of 5-bromo-2-(naphthalen-6-yl)pyridine, C15H10BrN

C15H10BrN, monoclinic, P21/c (no. 14), a = 14.6998(9) Å, b = 5.9337(4) Å, c = 14.6275(11) Å, β = 113.542(8)°, V = 1169.67(15) Å3, Z = 4, R gt(F) = 0.0396, wR ref(F 2) = 0.1103, T = 293(2) K.

Nickel-Catalyzed Suzuki-Miyaura Coupling of Aliphatic Amides

We report the Ni-catalyzed Suzuki-Miyaura coupling of aliphatic amide derivatives. Prior studies have shown that aliphatic amide derivatives can undergo Ni-catalyzed carbon-heteroatom bond formation but that Ni-mediated C-C bond formation using aliphatic amide derivatives has remained difficult. The coupling disclosed herein is tolerant of considerable variation with respect to both the amide-based substrate and the boronate coupling partner and proceeds in the presence of heterocycles and epimerizable stereocenters. Moreover, a gram-scale Suzuki-Miyaura coupling/Fischer indolization sequence demonstrates the ease with which unique polyheterocyclic scaffolds can be constructed, particularly by taking advantage of the enolizable ketone functionality present in the cross-coupled product. The methodology provides an efficient means to form C-C bonds from aliphatic amide derivatives using nonprecious-metal catalysis and offers a general platform for the heteroarylation of aliphatic acyl electrophiles.

Scope of regioselective Suzuki reactions in the synthesis of arylpyridines and benzylpyridines and subsequent intramolecular cyclizations to azafluorenes and azafluorenones

The current investigation on regioselective Suzuki reaction of 2,3-dihalopyridines and 2-halo-3-halomethyl pyridines has been studied and extended for azafluorenes and azafluorenones synthesis.

Efficient Ni-catalyzed conversion of phenols protected with 2,4,6-trichloro-1,3,5-triazine (TCT) to olefins

An efficient Ni(COD)₂/dppf catalyzed olefination of Ar-O-TCT as synthetic equivalents of aryl halides is described. Activation of C-O bonds in phenols as readily available compounds was achieved with 2,4,6-trichloro-1,3,5-triazine (TCT). This method provides practical access to 1,2-disubstituted olefins in high yields and high functional group compatibility.

Catalyst Selection Facilitates the Use of Heterocyclic Sulfinates as General Nucleophilic Coupling Partners in Palladium-Catalyzed Coupling Reactions

A range of 5- and 6-membered heterocycle-derived sulfinates are shown to be effective nucleophilic coupling partners with aryl chlorides and bromides using Pd(0) catalysis. The use of optimal reaction conditions, specifically incorporating a P(t-Bu)₂Me-derived Pd catalyst, allowed reactions to be performed at moderate temperatures and enabled the inclusion of a variety of sensitive functional groups. Challenging heterocyclic sulfinates, including pyrazine, pyridazine, pyrimidine, pyrazole, and imidazole, were all shown to perform well.

Design, Synthesis, and Application of Polymer-Supported Silicon-Transfer Agents for Cross-Coupling Reactions with Organolithium Reagents

The initial design, synthesis, and validation of polymer-supported siloxane transfer agents have been achieved that permit the direct use of organolithium reagents in the palladium-catalyzed cross-coupling reactions. Through rational design, two generations of polymer support were developed that significantly simplify product purification and the transfer agent recycling.

Exhaustive Suzuki-Miyaura reactions of polyhalogenated heteroarenes with alkyl boronic pinacol esters

A novel Suzuki-Miyaura protocol is described that enables the exhaustive alkylation of polychlorinated pyridines. This method facilitates a formal synthesis of normuscopyridine and the rapid assembly of a dumbbell shaped portion of a [2]rotaxane.

Pyridine sulfinates as general nucleophilic coupling partners in palladium-catalyzed cross-coupling reactions with aryl halides

Pyridine rings are ubiquitous in drug molecules; however, the pre-eminent reaction used to form carbon-carbon bonds in the pharmaceutical industry, the Suzuki-Miyaura cross-coupling reaction, often fails when applied to these structures. This phenomenon is most pronounced in 2-substituted pyridines, and results from the difficulty in preparing, the poor stability of, and low efficiency in reactions of pyridine-2-boronates. We demonstrate that by replacing these boronates with pyridine-2-sulfinates, a cross-coupling process of unrivalled scope and utility is realized. The corresponding 3- and 4-substituted pyridine variants are also efficient coupling partners. In addition, we apply these sulfinates in a library format to the preparation of medicinally relevant derivatives of the drugs varenicline (Chantix) and mepyramine (Anthisan).

An active catalytic system for Suzuki-Miyaura cross-coupling reactions using low levels of palladium loading

An easily available Pd(OAc)₂/(2-(anthracen-9-yl)-1H-inden-3-yl) dicyclohexylphosphine/toluene/ⁱPrOH/water catalytic system was developed, which shows high catalytic activity in the Suzuki-Miyaura cross-coupling reactions of a diverse array of aryl and heteroaryl chlorides with Pd loadings down to 0.01 mol%.

Synthesis of 3-Substituted 2-Arylpyridines via Cu/Pd-Catalyzed Decarboxylative Cross-Coupling of Picolinic Acids with (Hetero)Aryl Halides

A decarboxylative cross-coupling of 3-substituted picolinic acids with (hetero)aryl halides is presented. In the presence of catalytic Cu₂O and Pd(1,5-cyclooctadiene)Cl₂ with 2-dicyclohexylphosphino-2'-(N,N-dimethylamino)biphenyl as the ligand, both electron-rich and electron-deficient aryl bromides and chlorides as well as heteroaryl bromides were successfully coupled with various picolinate salts under mild conditions in yields up to 96%. This protocol provides an efficient entry to 2-(hetero)arylpyridines, an attractive substance class in drug discovery.