Synthesis of α-Aryl Esters and Nitriles: Deaminative Coupling of α-Aminoesters and α-Aminoacetonitriles with Arylboronic Acids

Synthesis of Secondary Boronates via Deaminative Cross-Coupling of Alkyl Nitroso Carbamates and Boronic Acids

A strategy for transition metal-free cross-coupling of alkyl nitroso-carbamates and boronic acids is reported. The N-nitroso carbamates are easily prepared from the corresponding amine in two simple steps. This method allows for the synthesis of a wide variety of secondary boronates, benzylic boronates and formal Csp3-Csp2 cross-coupling products under operationally simple conditions. Functional group tolerance is also demonstrated and applied in the modification of lysine to make non-canonical amino acids.

Mechanochemical synthesis of aromatic ketones: pyrylium tetrafluoroborate mediated deaminative arylation of amides

A new method has been introduced that is able to tackle the complexities of N-C(O) activation in amide moieties through utilization of pyrylium tetrafluoroborate in a mechanochemical setting, where amide bonds undergo activation and subsequent conversion to biaryl ketones. Due to the employment of a mechanochemical setting, the reaction conforms to green chemistry principles, offering an environmentally friendly approach to traditional amide derivatization techniques that rely on transition metals to achieve further functionalization.

Palladium-catalyzed dehydrogenation of α-cyclohexene-substituted nitriles to α-aryl nitriles

The development of a practical, inexpensive, and cyanide-free method for synthesizing α-aryl nitriles remains a challenging goal in synthetic chemistry. Here, we report an approach for synthesizing α-aryl nitriles toward achieving this goal, by which α-cyclohexenyl acetonitriles and α-cyclohexenyl alkenyl nitriles are dehydrogenated to α-aryl nitriles.

Synthesis of substituted benzylboronates by light promoted homologation of boronic acids with N-sulfonylhydrazones

The synthesis of benzylboronates by photochemical homologation of boronic acids with N-tosylhydrazones under basic conditions is described. The reaction involves the photolysis of the N-tosylhydrazone salt to give a diazoalkane followed by the geminal carboborylation of the diazoalkane. Under the mild reaction conditions, the protodeboronation of the unstable benzylboronic acid is circumvented and the pinacolboronates can be isolated after reaction of the benzylboronic acid with pinacol. The metholodogy has been applied to the reactions of alkylboronic acids with N-tosylhydrazones of aromatic aldehydes and ketones, and to the reactions of arylboronic acids with N-tosylhydrazones of aliphatic ketones. Moreover, the employment of the DBU/DIPEA bases combination allows for homogeneous reactions which have been adapted to photochemical continuous flow conditions. Additionally, the synthetic versatility of boronates enables their further transformation via Csp3-C or Csp3-X bond forming reactions converting this methodology into a novel method for the geminal difunctionalization of carbonyls via N-tosylhydrazones.

Visible-Light-Mediated Synthesis of α-Aryl Ester Derivatives via an EDA Complex

We report an efficient radical-based and photocatalyst-free method for the C(sp2)-C(sp3) cross-coupling reaction to synthesize α-aryl ester derivatives. The process starts from a β-keto ester and an electron-deficient halogenated aryl halide under alkaline conditions to form an electron donor-acceptor complex and is driven by visible light. From the synthetic point of view, this newly established method represents a simple way to access arylpropionic acids from commercially available and cheap starting materials.

Photocatalytic Three-Component Synthesis of 3-Heteroarylbicyclo[1.1.1]pentane-1-acetates

Herein, we report a visible-light-induced three-component reaction involving [1.1.1]propellane, diazoates, and various heterocycles for the synthesis of 3-heteroarylbicyclo[1.1.1]pentane-1-acetates. Throughout this reaction, the radicals generated from diazoate species react with [1.1.1]propellane in an addition reaction to form bicyclo[1.1.1]pentane (BCP) radicals that subsequently react with heterocycles, leading to the formation of 1,3-disubstituted BCP acetates. Notably, this methodology exhibits excellent functional group compatibility, high atom economy, and mild reaction conditions, thus facilitating suitable synthetic access to 1,3-disubstituted BCP acetates.

Boron Lewis Acid Catalysis Enables the Direct Cyanation of Benzyl Alcohols by Means of Isonitrile as Cyanide Source

The development of an efficient and straightforward method for cyanation of alcohols is of great value. However, the cyanation of alcohols always requires toxic cyanide sources. Herein, an unprecedented synthetic application of an isonitrile as a safer cyanide source in B(C₆F₅)₃-catalyzed direct cyanation of alcohols is reported. With this approach, a wide range of valuable α-aryl nitriles was synthesized in good to excellent yields (up to 98%). The reaction can be scaled up and the practicability of this approach is further manifested in the synthesis of an anti-inflammatory drug, naproxen. Moreover, experimental studies were performed to illustrate the reaction mechanism.

Computer-Driven Development of Ylide Functionalized Phosphines for Palladium-Catalyzed Hiyama Couplings

Palladium-catalyzed couplings of silicon enolates with aryl electrophiles are of great synthetic utility, but often limited to expensive bromide substrates. A comparative experimental study confirmed that none of the established ligand systems allows to couple inexpensive aryl chlorides with α-trimethylsilyl alkylnitriles. In contrast, ylide functionalized phosphines (YPhos) led to encouraging results. A statistical model was developed that correlates the reaction yields with ligand features. It was employed to predict catalyst structures with superior performance. With this cheminformatics approach, YPhos ligands were tailored specifically to the demands of Hiyama couplings. The newly synthesized ligands displayed record-setting activities, enabling the elusive coupling of aryl chlorides with α-trimethylsilyl alkyl nitriles. The preparative utility of the catalyst system was demonstrated by the synthesis of pharmaceutically meaningful α-aryl alkylnitriles, α-arylcarbonyls and biaryls.

Deaminative coupling of benzylamines and arylboronic acids

A metal-free deaminative coupling of non-prefunctionalised benzylamines and arylboronic acids is reported. In this operationally simple reaction, a primary amine in benzylamine is converted into a good leaving group in situ using inexpensive and commercially available isoamyl nitrite as a nitrosating reagent. Lewis-acidic arylboronic acids are shown to replace mineral acids such as HCl or HBF₄ that are conventionally used in the preparation of aryl diazonium salts. This unlocked the formation of the corresponding diarylmethanes by forging a new C-C bond in good yields.

Organocatalytic Oxidative C-H Amination of Aldehyde Hydrazones with Azoles at Ambient Temperature

An efficient, metal-free, and direct oxidative amination of aldehyde-derived hydrazones with azoles has been developed using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone as an organocatalyst at ambient temperature. This protocol provides a wide range of aminated hydrazone derivatives in a step and atom economical fashion. The reaction possibly follows a radical mechanism.

Rapid and Simple Access to α-(Hetero)arylacetonitriles from Gem-Difluoroalkenes

A scalable cyanation of gem-difluoroalkenes to (hetero)arylacetonitrile derivatives was developed. This strategy features mild reaction conditions, excellent yields, wide substrate scope, and broad functional group tolerance. Significantly, in this reaction, aqueous ammonia offers a "N" source for the "CN" reagent and entirely avoids the use of toxic cyanating reagents or metal catalysis. Hence, we provide a green and alternative method for the synthesis of arylacetonitriles.

Copper-Catalyzed Ullmann-Type Coupling and Decarboxylation Cascade of Arylhalides with Malonates to Access α-Aryl Esters

We have developed a high-efficiency and practical Cu-catalyzed cross-coupling to directly construct versatile α-aryl-esters by utilizing readily available aryl bromides (or chlorides) and malonates. These gram-scale approaches occur with turnovers of up to 1560 and are smoothly conducted by the usage of a low catalyst loading, a new available ligand, and a green solvent. A variety of functional groups are tolerated, and the application occurs with α-aryl-esters to access nonsteroidal anti-inflammatory drugs (NSAIDs) on the gram scale.

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.

An intramolecular coupling approach to alkyl bioisosteres for the synthesis of multisubstituted bicycloalkyl boronates

Bicyclic hydrocarbons, and bicyclo[1.1.1]pentanes (BCPs) in particular, are playing an emerging role as saturated bioisosteres in pharmaceutical, agrochemical and materials chemistry. Taking advantage of strain-release strategies, prior synthetic studies have featured the synthesis of bridgehead-substituted (C1, C3) BCPs from [1.1.1]propellane. Here, we describe an approach to access multisubstituted BCPs via intramolecular cyclization. In addition to C1,C3-disubstituted BCPs, this method also enables the construction of underexplored multisubstituted (C1, C2 and C3) BCPs from readily accessible cyclobutanones. The broad generality of this method has also been examined through the synthesis of a variety of other caged bicyclic molecules, ranging from [2.1.1] to [3.2.1] scaffolds. The modularity afforded by the pendant bridgehead boron pinacol esters generated during the cyclization reaction has been demonstrated through several downstream functionalizations, highlighting the ability of this approach to enable the programmed and divergent synthesis of multisubstituted bicyclic hydrocarbons.

Photocatalytic acyl azolium-promoted alkoxycarbonylation of trifluoroborates

Despite recent advancements in the selective generation and coupling of organic radical species, the alkoxycarbonyl radical remains underexplored relative to other carbon-containing radical species. Drawing inspiration from new strategies for generating acyl radical equivalents utilizing dual N-heterocyclic carbene catalysis and photocatalysis, we have prepared dimethylimidazolium esters that can function as an alkoxycarbonyl radical surrogate under photocatalytic conditions. We demonstrate the synthetic utility of these azolium-based partners through the preparation of esters arising from the coupling of this radical surrogate with an oxidatively generated alkyl radical.

Deaminative meta-C-H alkylation by ruthenium(ii) catalysis

Precise structural modifications of amino acids are of importance to tune biological properties or modify therapeutical capabilities relevant to drug discovery. Herein, we report a ruthenium-catalyzed meta-C–H deaminative alkylation with easily accessible amino acid-derived Katritzky pyridinium salts. Likewise, remote C–H benzylations were accomplished with high levels of chemoselectivity and remarkable functional group tolerance. The meta-C–H activation approach combined with our deaminative strategy represents a rare example of selectively converting C(sp³)–N bonds into C(sp³)–C(sp²) bonds.

Precise structural modifications of amino acids are of importance to tune biological properties or modify therapeutical capabilities relevant to drug discovery.

Assembly of α-(Hetero)aryl Nitriles via Copper-Catalyzed Coupling Reactions with (Hetero)aryl Chlorides and Bromides

α-(Hetero)aryl nitriles are important structural motifs for pharmaceutical design. The known methods for direct synthesis of these compounds via coupling with (hetero)aryl halides suffer from narrow reaction scope. Herein, we report that the combination of copper salts and oxalic diamides enables the coupling of a variety of (hetero)aryl halides (Cl, Br) and ethyl cyanoacetate under mild conditions, affording α-(hetero)arylacetonitriles via one-pot decarboxylation. Additionally, the CuBr/oxalic diamide catalyzed coupling of (hetero)aryl bromides with α-alkyl-substituted ethyl cyanoacetates proceeds smoothly at 60 °C, leading to the formation of α-alkyl (hetero)arylacetonitriles after decarboxylation. The method features a general substrate scope and is compatible with various functionalities and heteroaryls.

Coupling of Reformatsky Reagents with Aryl Chlorides Enabled by Ylide-Functionalized Phosphine Ligands

The coupling of aryl chlorides with Reformatsky reagents is a desirable strategy for the construction of α‐aryl esters but has so far been substantially limited in the substrate scope due to many challenges posed by various possible side reactions. This limitation has now been overcome by the tailoring of ylide‐functionalized phosphines to fit the requirements of Negishi couplings. Record‐setting activities were achieved in palladium‐catalyzed arylations of organozinc reagents with aryl electrophiles using a cyclohexyl‐YPhos ligand bearing an ortho‐tolyl‐substituent in the backbone. This highly electron‐rich, bulky ligand enables the use of aryl chlorides in room temperature couplings of Reformatsky reagents. The reaction scope covers diversely functionalized arylacetic and arylpropionic acid derivatives. Aryl bromides and chlorides can be converted selectively over triflate electrophiles, which permits consecutive coupling strategies.

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.

Reframing primary alkyl amines as aliphatic building blocks

While primary aliphatic amines are ubiquitous in natural products, they are traditionally considered inert to substitution chemistry. This review highlights historical and recent advances in the field of aliphatic deamination chemistry which demonstrate these moieties can be harnessed as valuable C(sp3) synthons. Cross-coupling and photocatalyzed transformations proceeding through polar and radical mechanisms are compared with oxidative deamination and other transition metal catalyzed reactions.

Practical and Modular Construction of C(sp3)-Rich Alkyl Boron Compounds

Alkyl boronic acids and esters play an important role in the synthesis of C(sp³)-rich medicines, agrochemicals, and material chemistry. This work describes a new type of transition-metal-free mediated transformation to enable the construction of C(sp³)-rich and sterically hindered alkyl boron reagents in a practical and modular manner. The broad generality and functional group tolerance of this method is extensively examined through a variety of substrates, including synthesis and late-stage functionalization of scaffolds relevant to medicinal chemistry. The strategic significance of this approach, with alkyl boronic acids as linchpins, is demonstrated through various downstream functionalizations of the alkyl boron compounds. This two-step concurrent cross-coupling approach, resembling formal and flexible alkyl-alkyl couplings, provides a general entry to synthetically challenging high Fsp³-containing drug-like scaffolds.

Transition-Metal-Free C(sp2 )-C(sp2 ) Cross-Coupling of Diazo Quinones with Catechol Boronic Esters

A transition-metal-free C(sp² )-C(sp² ) bond formation reaction by the cross-coupling of diazo quinones with catechol boronic esters was developed. With this protocol, a variety of biaryls and alkenyl phenols were obtained in good to high yields under mild conditions. The reaction tolerates various functionalities and is applicable to the derivatization of pharmaceuticals and natural products. The synthetic utility of the method was demonstrated by the short synthesis of multi-substituted triphenylenes and three bioactive natural products, honokiol, moracin M, and stemofuran A. Mechanistic studies and density functional theory (DFT) calculations revealed that the reaction involves attack of the boronic ester by a singlet quinone carbene followed by a 1,2-rearrangement through a stepwise mechanism.

Deaminative Arylation of Amino Acid-derived Pyridinium Salts

A Suzuki-Miyaura cross-coupling of α-pyridinium esters and arylboroxines has been developed. Combined with formation of the pyridinium salts from amino acid derivatives, this method enables amino acid derivatives to be efficiently transformed into α-aryl esters and amides. Under the mild conditions, broad functional group tolerance on both the amino acid derivatives and the arylboroxine are observed, including protic functional groups. Mechanistic studies support an alkyl radical intermediate, similar to other cross-couplings of alkylpyridinium salts.

Metal-free synthesis of gem-silylboronate esters and their Pd(0)-catalyzed cross-coupling with aryliodides

A transition-metal-free method for the synthesis of gem-silylboronate esters with arylboronic acids and trimethylsilyldiazomethane (TMSCHN2) has been developed. This transformation is a straightforward homologation of arylboronic acids and features wide substrate scope and good functional-group tolerance. The gem-silylboronate esters undergo efficient Suzuki-Miyaura cross-coupling with aryliodides and the silyl group of the product can be further functionalized. Tertiary carbon centers with different substituents can be constructed successfully by selective and sequential functionalization.

Metal-Free Denitrogenative C-C Couplings of Pyridotriazoles with Boronic Acids To Afford α-Secondary and α-Tertiary Pyridines

Pyridotriazoles are utilized as robust building blocks to access α-secondary and α-tertiary pyridines via the development of a simple yet practically useful metal-free denitrogenative C-C cross-coupling with boronic acids. The reaction shows a high level of functional tolerance, broad substrate scope, and facile scalability. The synthetic potential of the method is demonstrated by the strurctural modification of a bioactive molecule and concise synthesis of pheniramine analogs.

Harnessing Alkylpyridinium Salts as Electrophiles in Deaminative Alkyl-Alkyl Cross-Couplings

A Negishi cross-coupling of alkylpyridinium salts and alkylzinc halides has been developed. This is the first example of alkyl-alkyl bond formation via cross-coupling of an alkyl amine derivative with an unactivated alkyl group, and allows both primary and secondary alkylpyridinium salts to react with primary alkylzinc halides with high functional group tolerance. When combined with formation of the pyridinium salts from primary amines, this method enables the noncanonical transformation of NH2 groups into a wide range of alkyl substituents with broad functional group tolerance.

Transition metal-free direct dehydrogenative arylation of activated C(sp3)-H bonds: synthetic ambit and DFT reactivity predictions

A transition metal-free dehydrogenative method for the direct mono-arylation of a wide range of activated C(sp³)-H bonds has been developed. This operationally simple and environmentally friendly aerobic arylation uses tert-BuOK as the base and nitroarenes as electrophiles to prepare up to gram quantities of structurally diverse sets (>60 examples) of α-arylated esters, amides, nitriles, sulfones and triaryl methanes. DFT calculations provided a predictive model, which states that substrates containing a C(sp³)-H bond with a sufficiently low pK _a value should readily undergo arylation. The DFT prediction was confirmed through experimental testing of nearly a dozen substrates containing activated C(sp³)-H bonds. This arylation method was also used in a one-pot protocol to synthesize over twenty compounds containing all-carbon quaternary centers.

When diazo compounds meet with organoboron compounds

Transition-metal free reactions of diazo compounds with organoboron compounds provide some unique approaches for the formation of C–C, C–B and C–Si bonds. With N-tosylhydrazones as the precursors for non-stabilized diazo compound, this type of reaction becomes practically useful in organic synthesis. Transition-metal-free synthetic methodologies for borylation, gem-diborylation, gem-silylborylation arylation, 2,2,2-trifluoroethylation and gem-difluorovinylation have been successfully developed.

Harnessing Alkyl Amines as Electrophiles for Nickel-Catalyzed Cross Couplings via C-N Bond Activation

We developed a strategy to harness alkyl amines as alkylating agents via C-N bond activation. This Suzuki-Miyaura cross coupling of alkylpyridinium salts, readily formed from primary amines, is the first example of a metal-catalyzed cross coupling via C-N bond activation of an amine with an unactivated alkyl group. This reaction enjoys broad scope and functional group tolerance. Primary and secondary alkyl groups can be installed. Preliminary studies suggest a NiI/NiIII catalytic cycle.

Palladium-Catalyzed, ortho-Selective C-H Halogenation of Benzyl Nitriles, Aryl Weinreb Amides, and Anilides

A palladium-catalyzed, ortho-selective C-H halogenation methodology is reported herein. The highlight of the work is the highly selective C(sp²)-H functionalization of benzyl nitriles in the presence of activated C(sp³)-H bond, which results in good yields of the halogenated products with excellent regioselectivity. Along with benzyl nitriles, aryl Weinreb amides and anilides have been evaluated for the transformation using aprotic conditions. Mechanistic studies yield interesting aspects with respect to the pathway of the reaction and the directing group abilities.

Discovery of a Flexible Triazolylbutanoic Acid as a Highly Potent Uric Acid Transporter 1 (URAT1) Inhibitor

In order to systematically explore and understand the structure–activity relationship (SAR) of a lesinurad-based hit (1c) derived from the replacement of the S atom in lesinurad with CH₂, 18 compounds (1a–1r) were designed, synthesized and subjected to in vitro URAT1 inhibitory assay. The SAR exploration led to the discovery of a highly potent flexible URAT1 inhibitor, 1q, which was 31-fold more potent than parent lesinurad (IC₅₀ = 0.23 μM against human URAT1 for 1q vs 7.18 μM for lesinurad). The present study discovered a flexible molecular scaffold, as represented by 1q, which might serve as a promising prototype scaffold for further development of potent URAT1 inhibitors, and also demonstrated that the S atom in lesinurad was not indispensable for its URAT1 inhibitory activity.