Carbon-based Nucleophiles Research Articles

A Practical Guide to SuFEx Chemistry: An Overview of S(VI)-SuFEx Linkers and Their Reactivity

AbstractSulfur(VI)–fluoride exchange (SuFEx) is a second generation, metal-free click chemistry concept introduced by Sharpless in 2014. Since the introduction of the concept, a large variety of synthetic methodologies to S(VI)-SuFEx hubs, and their derivatization with oxygen-, nitrogen-, and carbon-based nucleophiles have been developed. Herein, we provide a concise and practical overview for their preparation, SuFExability, inclusive of which substituents are tolerated. The stereoselective synthesis of aza-derivatives is also discussed.1 Introduction2 Synthesis of SuFEx Hubs2.1 Sulfonyl Fluorides2.2 Fluorosulfates2.3 Sulfamoyl Fluorides2.4 Sulfonimidoyl Fluorides2.5 Sulfuramidimidoyl Fluorides and Sulfurofluoridoimidates2.6 Sulfondiimidoyl Fluorides3 Reactivity of SuFEx Hubs3.1 Reactivity of Sulfonyl Fluorides3.2 Reactivity of Fluorosulfates3.3 Reactivity of Sulfamoyl Fluorides3.4 Reactivity of Sulfonimidoyl Fluorides3.5 Reactivity of Sulfurofluoridoimidates3.6 Reactivity of Sulfondiimidoyl Fluorides4 Stereochemical Considerations in SuFEx Chemistry5 Conclusion and Outlook

Synthesis of 1,3-Dicarbonyl Azepines via Photoinitiated Reactions of Aryl Azides with Carbon-Based Nucleophiles.

A photoinduced one-pot method for the synthesis of azepines by the reaction of aryl azides with 1,3-dicarbonyl compounds under weakly basic conditions is described. This method offers a simple route for the synthesis of 1,3-dicarbonyl-substituted azepines in good to excellent yields and high regioselectivity and was tested on 1,3-dicarbonyl compounds with different acidity levels. The resulting azepines have electrophilic and nucleophilic centers of varying degrees of activity, which facilitate reactions leading to further structural transformations.

Oxidative Dearomatization of Pyridines.

Dearomatization of pyridines is a well-established synthetic approach to access piperidines. Although remarkably powerful, existing dearomatization processes have been limited to the hydrogenation or addition of carbon-based nucleophiles to activated pyridiniums. Here, we show that arenophile-mediated dearomatizations can be applied to pyridines to directly introduce heteroatom functionalities without prior substrate activation. The arenophile platform in combination with olefin oxidation chemistry provides access to dihydropyridine cis-diols and epoxides. These previously elusive compounds are now readily accessible and can be used for the downstream preparation of diversely functionalized piperidines.

Nucleophilic Attack at Pentaarsaferrocene [Cp*Fe(η5 -As5 )]-The Way to Larger Polyarsenide Ligands.

By the reaction of [Cp*Fe(η5 -As5 )] (I) (Cp*=C5 Me5 ) with main group nucleophiles, unique functionalized products with η4 -coordinated polyarsenide (Asn ) units (n=5, 6, 20) are obtained. With carbon-based nucleophiles such as MeLi or KBn (Bn=CH2 Ph), the anionic organo-substituted polyarsenide complexes, [Li(2.2.2-cryptand)][Cp*Fe(η4 -As5 Me)] (1 a) and [K(2.2.2-cryptand)][Cp*Fe{η4 -As5 (CH2 Ph)}] (1 b), are accessible. The use of KAsPh2 leads to a selective and controlled extension of the As5 unit and the formation of the monoanionic compound [K(2.2.2-cryptand][Cp*Fe(η4 -As6 Ph2 )] (2). When I is reacted with [M]As(SiMe3 )2 (M=Li ⋅ THF; K), the formation of the largest known anionic polyarsenide unit in [M'(2.2.2-cryptand)]2 [(Cp*Fe)4 {μ5 -η4 :η4 :η3 :η3 :η1 :η1 -As20 }] (3) occurred (M'=Li (3 a), K (3 b)).

Copper-catalyzed conjugate addition of allene-derived nucleophiles to alkenyl-substituted carboxamides

Catalytic Michael addition reaction represents a fundamental importance in organic synthetic chemistry. Whereas corresponding conversions toward intrinsically low reactive enamide remains an ongoing challenging. We herein report a copper-catalyzed conjugate addition of allenes to β-substituted alkenyl amides, one of the most challenging Michael acceptors. The present method utilizes readily available allenes as the latent carbon-based nucleophiles and simple, common β-substituted alkenyl amides as starting materials, unlike previous methods that usually preinstall an activating group to improve the reactivity of amide or uses highly reactive stoichiometric quantities of organometallics. Hence, this approach shows good functional group compatibility and can be implemented under mild reaction conditions with excellent level of chemo- and regioselectivities.

Use of (E,E)-Dienoic Acids as Switchable (E,E)- and (Z,E)-Dienyl Anion Surrogates via Ligand-Controlled Palladium Catalysis.

Carboxylic acids are not readily applied as carbon-based nucleophiles due to their intrinsic acidic group. Here, we demonstrate that free (E,E)-2,4-dienoic acids form electron-neutral and highest occupied molecular orbital-raised η2-complexes with Pd(0) and undergo Friedel-Crafts-type additions to imines with exclusive α-regioselectivity, giving formal dienylated products after decarboxylation. Unusual and switchable (E,E)- and (Z,E)-selectivity, along with excellent enantioselectivity, is achieved via ligand-controlled outer-sphere or inner-sphere reaction modes, respectively, which are well supported by comprehensive density functional theory calculation studies. An unprecedented formal reductive Mannich reaction between (E,E)-dienoic acids and imines is also developed to furnish enantioenriched β-amino acid derivatives.

An Expedient Method for the Umpolung Coupling of Enols with Heteronucleophiles.

In this paper, we present an unprecedented and general umpolung protocol that allows the functionalization of silyl enol ethers and of 1,3‐dicarbonyl compounds with a large range of heteroatom nucleophiles, including carboxylic acids, alcohols, primary and secondary amines, azide, thiols, and also anionic carbamates derived from CO2. The scope of the reaction also extends to carbon‐based nucleophiles. The reaction relies on the use of 1‐bromo‐3,3‐dimethyl‐1,3‐dihydro‐1λ3[d][1,2]iodaoxole, which provides a key α‐brominated carbonyl intermediate. The reaction mechanism has been studied experimentally and by DFT, and we propose formation of an unusual enolonium intermediate with a halogen‐bonded bromide.

Accessing Monosubstituted Cyclopentadienyl Rhodium(I) and Iridium(I) Complexes by a Simultaneous Nucleophilic Addition-Metalation Approach to Fulvenes

Despite advances in the synthesis of polysubstituted cyclopentadienyl metal complexes, the rapid access to a library of monosubstituted Cp bearing metal complexes remains challenging. A convenient and general method to access a broad range of monosubstituted cyclopentadienyl rhodium(I) and iridium(I) complexes is reported. The process involves a direct nucleo-metalation of fulvenes with widely available metal precursors, affording a set of CpRhI(olefin)2 and CpIrI(olefin)2 complexes in high yields. A broad range of oxygen-, nitrogen-, and carbon-based nucleophiles were found competent for the process and offer good tuning abilities of the cyclopentadienyl portion.

General Synthesis of Trialkyl- and Dialkylarylsilylboranes: Versatile Silicon Nucleophiles in Organic Synthesis.

Compared to carbon-based nucleophiles, the number of silicon-based nucleophiles that is currently available remains limited, which significantly hampers the structural diversity of synthetically accessible silicon-based molecules. Given the high synthetic utility and ease of handling of carbon-based boron nucleophiles, silicon-based boron nucleophiles, i.e., silylboranes, have attracted considerable interest in recent years as nucleophilic silylation reagents that are activated by transition-metal catalysts or bases. However, the range of practically accessible silylboranes remains limited. In particular, the preparation of sterically hindered and functionalized silylboranes remains a significant challenge. Here, we report the use of rhodium and platinum catalysts for the direct borylation of hydrosilanes with bis(pinacolato)diboron, which allows the synthesis of new trialkylsilylboranes that bear bulky alkyl groups and functional groups as well as new dialkylarylsilylboranes that are difficult to synthesize via conventional methods using alkali metals. We further demonstrate that these compounds can be used as silicon nucleophiles in organic transformations, which significantly expands the scope of synthetically accessible organosilicon compounds compared to previously reported methods. Thus, the present study can be expected to inspire the development of efficient methods for novel silicon-containing bioactive molecules and organic materials with desirable properties. We also report the first 11B{1H} and 29Si{1H} NMR spectroscopic evidence for the formation of i-Pr3SiLi generated by the reaction of i-Pr3Si-B(pin) with MeLi.

Electrophilically Activated Nitroalkanes in Reactions With Carbon Based Nucleophiles

Unusual reactivity of nitroalkanes, involving formation of aci-forms (nitronic acids or nitronates) and their subsequent interaction with carbon-based nucleophiles, is surveyed in this review.

Catalytic Enantioselective Addition of an Allyl Group to Ketones Containing a Tri-, a Di-, or a Monohalomethyl Moiety. Stereochemical Control Based on Distinctive Electronic and Steric Attributes of C-Cl, C-Br, and C-F Bonds.

We disclose the results of an investigation designed to generate insight regarding the differences in the electronic and steric attributes of C-F, C-Cl, and C-Br bonds. Mechanistic insight has been gleaned by analysis of variations in enantioselectivity, regarding the ability of electrostatic contact between a halomethyl moiety and a catalyst's ammonium group as opposed to factors lowering steric repulsion and/or dipole minimization. In the process, catalytic and enantioselective methods have been developed for transforming a wide range of trihalomethyl (halogen = Cl or Br), dihalomethyl, or monohalomethyl (halogen = F, Cl, or Br) ketones to the corresponding tertiary homoallylic alcohols. By exploiting electrostatic attraction between a halomethyl moiety and the catalyst's ammonium moiety and steric factors, high enantioselectivity was attained in many instances. Reactions can be performed with 0.5-5.0 mol % of an in situ generated boryl-ammonium catalyst, affording products in 42-99% yield and up to >99:1 enantiomeric ratio. Not only are there no existing protocols for accessing the great majority of the resulting products enantioselectively but also in some cases there are hardly any instances of a catalytic enantioselective addition of a carbon-based nucleophile (e.g., one enzyme-catalyzed aldol addition involving trichloromethyl ketones, and none with dichloromethyl, tribromomethyl, or dibromomethyl ketones). The approach is scalable and offers an expeditious route to the enantioselective synthesis of versatile and otherwise difficult to access aldehydes that bear an α-halo-substituted quaternary carbon stereogenic center as well as an assortment of 2,2-disubstituted epoxides that contain an easily modifiable alkene. Tertiary homoallylic alcohols containing a triazole and a halomethyl moiety, structural units relevant to drug development, may also be accessed efficiently with exceptional enantioselectivity.

Divergent Synthesis of Enantioenriched β-Functional Amines via Desymmetrization of meso-Aziridines with Isocyanides.

A highly enantioselective ring-opening desymmetrization of meso-aziridines with isocyanides was achieved in the presence of a chiral N,N'-dioxide/Mg(OTf)2 complex. The in situ generated chiral 1,4-zwitterionic intermediates were successfully trapped by intramolecular oxygen- and carbon-based nucleophiles or exogenous H2O and TMSN3, enabling a collective synthesis of various chiral vicinal amino-oxazoles, spiroindolines, β-amino amides, and tetrazole derivative in moderate to high yields with excellent enantioselectivities.

Halogen-Bond-Catalyzed Addition of Carbon-Based Nucleophiles to N-Acylimminium Ions.

N-acylimminium ions are an important class of synthetic intermediates to produce diverse products upon treatment with different nucleophiles. Most of the reported catalytic protocol involved moisture-sensitive Lewis acids or transition metal. Herein, we reported an organocatalytic version by using halogen-bond catalyst as mild Lewis acid through anion-abstraction strategy. A preliminary result of enantioselective version by employing a chiral BINOL-phosphate anion has also been demonstrated.

A Novel, Efficient, and Recoverable Basic Fe3O4@C Nano-Catalyst for Green Synthesis of 4H-Chromenes in Water via One-Pot Three Component Reactions

A novel basic carbon coated magnetic nanoparticles (BCCMNPs-VI; Fe3O4@C@ONa) were designed and synthesized by a facile and inexpensive two steps procedure. The BCCMNPs-VI were prepared trough synthesis and treatment of Fe3O4@C by NaOH. It could play a key role as an efficient, environmentally friendly, and easily recoverable catalyst in a one-pot, three-component reaction of salicylaldehyde, active methylene, and carbon-based nucleophile in water that led to green synthesis of 4H-chromenes. Nontoxic and inexpensive materials and solvent usage, short time, simple work-up, excellent yield as well as easily recoverable catalyst by an external magnet have made the method featured. The stability, and reusability of recycled nanocatalyst were investigated after nine runs. The synthesized magnetic nanocatalyst was characterized by FTIR, XRD, VSM, FE-SEM, TEM, EDX, XRD, TGA, DTG, DSC, and ICP-OES analyses.

Delayed catalyst function enables direct enantioselective conversion of nitriles to NH2-amines.

Accessing enantiomerically enriched amines often demands oxidation-state adjustments, protection and deprotection processes, and purification procedures that increase cost and waste, limiting applicability. When diastereomers can be formed, one isomer is attainable. Here, we show that nitriles, largely viewed as insufficiently reactive, can be transformed directly to multifunctional unprotected homoallylic amines by enantioselective addition of a carbon-based nucleophile and diastereodivergent reduction of the resulting ketimine. Successful implementation requires that competing copper-based catalysts be present simultaneously and that the slower-forming and less reactive one engages first. This challenge was addressed by incorporation of a nonproductive side cycle, fueled selectively by inexpensive additives, to delay the function of the more active catalyst. The utility of this approach is highlighted by its application to the efficient preparation of the anticancer agent (+)-tangutorine.

An efficient method for the synthesis of functionalized 4H-chromenes as optical sensor for detection of Fe3+ in ethanol

An efficient method for the synthesis of functionalized 4H-chromenes via a one-pot three-component condensation reaction of a 2-hydroxybenzaldehyde with an active methylene compound and a carbon-based nucleophile in the presence of SrFe12O19 as catalyst under solvent-free at 80 °C condition has been described. SrFe12O19 was an efficient, green, and reusable magnetic nanoparticles as heterogeneous catalyst with the average particles size of 70 nm which can be recycled and readily separated from the reaction mixture using an external magnet. High product yields, simple work-up procedure, solvent-free conditions and characterization of the sensing properties of compound 4a for detection of Fe3+ ion are the main advantages of this procedure. The sensing ability of compound 4a was examined upon addition of a wide variety of cations both visually and by UV–Vis spectroscopy. The increase in UV–Vis absorbance was linearly proportional to the concentration of Fe3+ with a detection limit of 1.0 × 10−7 M. Moreover, the chemosensor exhibited an obvious color change from white to yellow in the presence of Fe3+ in EtOH solution.

Directed, Palladium(II)-Catalyzed Enantioselective anti-Carboboration of Alkenyl Carbonyl Compounds

A substrate-directed enantioselective anti-carboboration reaction of alkenes has been developed, wherein a carbon-based nucleophile and a boron moiety are installed across the C=C bond through a 5-membered palladacycle intermediate. A preliminary result also shows it is possible to extend this reaction to alkenes that are more distal from the directing group and react via a 6-membered palladacycle. The reaction is promoted by a palladium(II) catalyst and a monodentate oxazoline ligand. A range of enantioenriched secondary alkylboronate products were obtained with moderate to high enantioselectivity that could be further upgraded by recrystallization. This work represents an efficient method to synthesize versatile and valuable alkylboronate building blocks. Building on an earlier mechanistic proposal by Peng, He, and Chen, a revised model is proposed to account for the stereoconvergent nature of this transformation.

One and Two-Carbon Homologation of Primary and Secondary Alcohols to Corresponding Carboxylic Esters Using β-Carbonyl BT Sulfones as a Common Intermediate.

Herein we report the efficient one- and two-carbon homologation of 1° and 2° alcohols to their corresponding homologated esters via the Mitsunobu reaction using β-carbonyl benzothiazole (BT) sulfone intermediates. The one-carbon homologation approach uses standard Mitsunobu C-S bond formation, oxidation and subsequent alkylation, while the two-carbon homologation uses a less common C-C bond forming Mitsunobu reaction. In this latter case, the use of β-BT sulfone bearing esters lowers the p Ka sufficiently enough for the substrate to be used as a carbon-based nucleophile and deliver the homologated β-BT sulfone ester, and this superfluous sulfone group can then be cleaved. In this paper we describe several methods for the effective desulfonylation of BT sulfones and have developed methodology for one-pot alkylation-desulfonylation sequences. As such, overall, a one-carbon homologation sequence can be achieved in a two-pot (four step) procedure and the two-carbon homologation in a two-pot (three step) procedure (three-pot; four step when C-acid synthesis is included). This methodology has been applied to a wide variety of functionality (esters, silyl ethers, benzyls, heteroaryls, ketones, olefins and alkynes) and are all tolerated well providing good to very good overall yields. The power of our method was demonstrated in site-selective ingenol C20 allylic alcohol two-carbon homologation.

Electrophilic Metal Homoenolates and Their Application in the Synthesis of Cyclopropylamines

Since their discovery, metal homoenolates have been widely explored as carbon-based nucleophiles for the β-functionalization of carbonyl derivatives. Only recently has it been reported that metal ­homoenolates can react as carbonyl electrophiles. In this context, we have recently discovered that cyclopropylamines can be prepared from cyclopropanols via zinc homoenolate intermediates. This Synpacts ­article will present an overview of the reactivity of homoenolates and our strategy to employ these intermediates for the synthesis of cyclopropylamines. Key mechanistic observations and their influence on reaction optimization will also be discussed.1 Introduction2 Homoenolates as Nucleophiles—Selected Reactivity3 Homoenolates as Electrophilic Reagents4 Conclusion

Catalytic diastereo- and enantioselective additions of versatile allyl groups to N-H ketimines.

There are many biologically active organic molecules that contain one or more nitrogen-containing moieties, and broadly applicable and efficient catalytic transformations that deliver them diastereoselectively and/or enantioselectively are much sought after. Various methods for enantioselective synthesis of α-secondary amines are available (for example, from additions to protected/activated aldimines), but those involving ketimines are much less common. There are no reported additions of carbon-based nucleophiles to unprotected/unactivated (or N-H) ketimines. Here, we report a catalytic, diastereo- and enantioselective three-component strategy for merging an N-H ketimine, a monosubstituted allene and B2(pin)2, affording products in up to 95% yield, >98% diastereoselectivity and >99:1 enantiomeric ratio. The utility of the approach is highlighted by synthesis of the tricyclic core of a class of compounds that have been shown to possess anti-Alzheimer activity. Stereochemical models developed with the aid of density functional theory calculations, which account for the observed trends and levels of enantioselectivity, are presented.