Sensitive Functional Groups Research Articles

Synthesis of gem-Difluoroalkenes via Nickel-Catalyzed Reductive C–F and C–O Bond Cleavage

By merging C–O and C–F bond cleavage in cross-electrophile coupling, we developed a method for efficient synthesis of gem-difluoroalkenes with an alkoxy-substituent on the homoallylic position using easily accessible acetals as coupling partners with α-trifluoromethyl alkenes. Remarkably, this Ni-catalyzed allylic defluorinative cross-coupling reaction demonstrates high tolerance of a wide range of sensitive functional groups and proves to be applicable in late-stage functionalization of structurally complex compounds.

Copper(II)-Catalyzed Reaction of 2,3-Allenoic Acids, Sulfur Dioxide, and Aryldiazonium Tetrafluoroborates: Route to 4-Sulfonylated Furan-2(5 H)-ones.

A copper(II)-catalyzed three-component reaction of 2,3-allenoic acids, sulfur dioxide, and aryldiazonium tetrafluoroborates under mild conditions is developed, leading to 4-sulfonylated furan-2(5 H)-ones in good yields. Not only sodium metabisulfite but also 1,4-diazabicyclo[2.2.2]octane-sulfur dioxide (DABCO·(SO2)2) is workable under the conditions. This transformation proceeds through a radical process initiated by the addition of arylsulfonyl radical to the C-central position of 2,3-allenoic acid. A broad substrate scope is demonstrated, and many sensitive functional groups are tolerated.

Arylzinc Halides by Silver Catalyzed Zinc Insertion into Aryl Iodides

A catalytic amount of silver acetate efficiently promotes direct insertion of zinc metal into aryl iodides, having different structure, in ethereal solvent. Electron‐rich substrates also rapidly undergo oxidative metalation. The arylzinc iodides formed give Negishi coupling products under mild reaction conditions to obtain biaryls in high yields. Sensitive functional groups like aldehydes and primary amides are well‐tolerated.

Phenolate Enabled General and Selective Fe/Ti Cocatalyzed Biaryl Cross-Couplings between Aryl Halides and Aryl Grignard Reagents.

The serendipitous addition of a phenolate to FeCl3/TMEDA/Ti(OEt)4 enables a strong Fe/Ti cooperativity that can efficiently catalyze a general and selective biaryl-coupling reaction. In the absence of phosphine or NHC ligands, various aryl chlorides, bromides, and iodides can couple with a variety of common and Knochel-type aryl Grignard reagents. A wide range of sensitive functional groups in either coupling partner can be tolerated. This bimetallic cocatalysis not only remarkably extends the scope of Fe-catalyzed biaryl couplings but also provides a solution to the problem of functional group compatibility of Grignard reagents.

Synthesis of Amides by Mild Palladium-Catalyzed Aminocarbonylation of Arylsilanes with Amines Enabled by Copper(II) Fluoride.

A general Pd-catalyzed synthesis of amides by oxidative aminocarbonylation of arylsilanes under mild conditions was accomplished for the first time. The reaction is promoted by a commercially available copper(II) fluoride, which acts as a dual silane activator and mild oxidant, enabling highly efficient aminocarbonylation of versatile arylsilanes at atmospheric CO pressure. The reaction is tolerant of a wide range of arylsilanes and various sensitive halide functional groups as well as a broad scope of amines are compatible with this oxidative process using cheap CO. A significant aspect involves the increased efficiency by the catalyst system. The reaction represents a segue into the powerful Pd-catalyzed oxidative transformations of organosilanes.

Acyl/aroyl Meldrum’s acid as an enol surrogate for the direct organocatalytic synthesis of α,β-unsaturated ketones

The operationally simple, robust and straightforward organocatalytic protocol is developed for the synthesis of E-selective α,β-unsaturated ketones. The method utilizes simple and easily accessible starting materials such as Meldrum’s acid, carboxylic acid, aldehyde and simple bifunctional amine catalyst. The tandem organocatalytic process utilizes acyl/aroyl Meldrum’s acid as an enol surrogate for the effective Doebner-Knoevenagel type condensation reactions. A wide variety of aldehydes, carboxylic acids and base sensitive functional groups are well tolerated under the mild reaction conditions.

CuI/l-proline catalyzed click reaction in glycerol for the synthesis of 1,2,3-triazoles

Despite the apparent simplicity of the copper(I) iodide catalyzed CuAAC reaction, the conversion of the catalytic species, i.e. Cu(I) to thermodynamically more stable Cu(II), via aerial oxidation or disproportionation is a major issue. To stabilize the Cu(I) species, the reaction is ideally carried out under an inert atmosphere in the presence of additives such as alcohols, amines, thiols, and aldehydes. Herein, we report the first CuI catalyzed click reaction without an inert atmosphere by employing the CuI/l-proline system in glycerol. The method showed remarkable stability towards sensitive functional groups such as acetonides and 1,2,4-trioxanes.

Highly chemoselective hydrogenation of nitroarenes catalyzed by 3,6-di(pyridin-2-yl)-1,2,4,5-s-tetrazine capped‑silver nanoparticles in aqueous medium at room temperature

3,6-Di(pyridin-2-yl)-1,2,4,5-s-tetrazine capped‑silver nanoparticles (TzAgNPs) exhibit an excellent catalytic activity and chemoselectivity for the reduction of various substituted nitroarenes to the corresponding aromatic amines in aqueous medium with sodium borohydride and hydrazine hydrate as a hydrogen donor at room temperature. The reaction kinetics of the reduction of 4-nitrophenol to 4-aminophenol has also been studied to determine the apparent rate constant. The catalyst TzAgNPs efficiently reduces the nitro group under very mild conditions, thus affording excellent yields within very short reaction time (˂20 min), and shows high selectivity even in the presence of other sensitive functional groups.

A flow platform for degradation-free CuAAC bioconjugation

The Cu-catalyzed azide-alkyne cycloaddition (CuAAC) reaction is a cornerstone method for the ligation of biomolecules. However, undesired Cu-mediated oxidation and Cu-contamination in bioconjugates limits biomedical utility. Here, we report a generic CuAAC flow platform for the rapid, robust, and broad-spectrum formation of discrete triazole bioconjugates. This process leverages an engineering problem to chemical advantage: solvent-mediated Cu pipe erosion generates ppm levels of Cu in situ under laminar flow conditions. This is sufficient to catalyze the CuAAC reaction of small molecule alkynes and azides, fluorophores, marketed drug molecules, peptides, DNA, and therapeutic oligonucleotides. This flow approach, not replicated in batch, operates at ambient temperature and pressure, requires short residence times, avoids oxidation of sensitive functional groups, and produces products with very low ppm Cu contamination.

Scalable and Chemoselective Synthesis of γ-Keto Esters and Acids via Pd-Catalyzed Carbonylation of Cyclic β-Chloro Enones

The Pd-catalyzed carbonylation of cyclic β-chloro enones using simple phosphine ligands is described. Screening identified P(Me)(t-Bu)2 as the most general ligand for an array of chloro enone electrophiles. The reaction scope has been evaluated on a milligram scale across 80 examples, with excellent reactivity observed in nearly every case. Carbonylation can be achieved even in the presence of potentially sensitive or inhibitory functional groups, including basic nitrogens as well as aryl chlorides or bromides. Twenty examples have been run on a gram scale, demonstrating scalability and practical utility. Using P(Me)(t-Bu)2, the reaction rate depends on both nucleophile and electrophile identity, with completion times varying between 3 and >18 h under a standard set of conditions. Switching to P(t-Bu)3 for the carbonylation of 3-chlorocyclohex-2-enone with methanol results in a dramatic rate increase, enabling effective catalysis with kinetics consistent with rate-limiting mass transfer. Stoichiometric ox...

Synthesis of gem-Difluoroalkenes via Nickel-Catalyzed Allylic Defluorinative Reductive Cross-Coupling

In this protocol, we report an allylic defluorinative reductive cross-coupling reaction for C–C bond formation. Under the Ni-catalysis the challenging C(sp3)–F bond cleavage of trifluoromethyl-substituted alkenes was achieved with easily accessible primary, secondary and tertiary alkyl halides as the coupling partners and Zn-powder as reducing agent. This process provides an efficient and convenient entry to gem-difluoroalkenes bearing various sensitive functional groups under mild reaction conditions. Moreover, this method proves to be suitable for late-stage functionalization of multifunctional complex molecules.

Cobalt-Catalyzed Aerobic Oxidative C–H/C–H Cross-Coupling of Unactivated Arenes for the Synthesis of Biaryls

A mild and efficient protocol for the synthesis of 2,2'-difunctional biaryls from readily available benzamides and oximes by Co(OAc)2·4H2O catalysis has been developed. The catalytic cycle that includes aerobic oxidation of Co(I) to Co(III) is successfully achieved for the first time through dual-chelation-assisted C-H/C-H coupling with the assistance of catalytic Mn(acac)3. The catalytic system exhibits powerful reactivity and tolerates a large number of sensitive functional groups.

Ir-Catalyzed Selective Hydroboration of 2-Substituted 1,3-Dienes: A General Method to Access Homoallylic Boronates

An operationally simple protocol for the 4,3-selective hydroboration of 2-substituted 1,3-dienes using an iridium catalyst is described. Independently of the nature (alkyl, aryl, heteroaryl) and the size of the substituent in the 2-position, it provides access to a variety of homoallylic boronates featuring a 1,1-disubstituted olefin in high yield and chemo- and regioselectivity. An array of potentially sensitive functional groups is well-tolerated, and the method can be extend to 1,2-disubstituted 1,3-dienes. Derivatization of the homoallylic boronates is also demonstrated using contemporary catalytic and enantioselective processes.

Ligand Free Approach for the Copper(II)‐Mediated C‐NH2 Arylation of 4‐Quinolone Derivatives Under Ambient Condition

AbstractCopper (II)‐mediated C‐NH2 arylation of both unprotected and protected 4‐quinolones under ambient condition has been developed. This is a ligand free, room temperature, rapid reaction protocol and found compatible with various sensitive functional groups. Moreover using this protocol, we have synthesized a library of diverse functionalized 4‐quinolone derivatives.

Iridium-Catalyzed Reductive Alkylations of Secondary Amides.

Reported herein is the first direct, metal-catalyzed reductive functionalization of secondary amides to give functionalized amines and heterocycles. The method is shown to have exceptionally broad scope with respect to suitable nucleophiles, which cover both hard and soft C nucleophiles as well as a P nucleophile. The reaction exhibits good chemoselectivity and tolerates several sensitive functional groups.

Iridium‐Catalyzed Reductive Alkylations of Secondary Amides

AbstractReported herein is the first direct, metal‐catalyzed reductive functionalization of secondary amides to give functionalized amines and heterocycles. The method is shown to have exceptionally broad scope with respect to suitable nucleophiles, which cover both hard and soft C nucleophiles as well as a P nucleophile. The reaction exhibits good chemoselectivity and tolerates several sensitive functional groups.

Divergent Reactivity of gem-Difluoro-enolates toward Nitrogen Electrophiles: Unorthodox Nitroso Aldol Reaction for Rapid Synthesis of α-Ketoamides.

An amination reaction of in situ generated gem-difluoro-enolates has been explored with electrophilic nitrogen sources. While their exposure to azodicarboxylates smoothly produced fluorinated α-amino ketones, reaction with nitrosoarenes (nitroso aldol reaction) furnished α-ketoamides in very high yields (up to 94%). The reaction is very fast (typically completed within 5 min) and scalable and tolerates various sensitive functional groups. Synthetic utility of this process was highlighted through the production of diverse nitrogen heterocycles and an orexin receptor antagonist.

Multicatalytic Stereoselective Synthesis of Highly Substituted Alkenes by Sequential Isomerization/Cross-Coupling Reactions.

Starting from readily available alkenyl methyl ethers, the stereoselective preparation of highly substituted alkenes by two complementary multicatalytic sequential isomerization/cross-coupling sequences is described. Both elementary steps of these sequences are challenging processes when considered independently. A cationic iridium catalyst was identified for the stereoselective isomerization of allyl methyl ethers and was found to be compatible with a nickel catalyst for the subsequent cross-coupling of the in situ generated methyl vinyl ethers with various Grignard reagents. The method is compatible with sensitive functional groups and a multitude of olefinic substitution patterns to deliver products with high control of the newly generated C═C bond. A highly enantioselective variant of this [Ir/Ni] sequence has been established using a chiral iridium precatalyst. A complementary [Pd/Ni] catalytic sequence has been optimized for alkenyl methyl ethers with a remote C═C bond. The final alkenes were isolated with a lower level of stereocontrol. Upon proper choice of the Grignard reagent, we demonstrated that C( sp2)-C( sp2) and C( sp2)-C( sp3) bonds can be constructed with both systems delivering products that would be difficult to access by conventional methods.

Organocatalyzed, Visible-Light Photoredox-Mediated, One-Pot Minisci Reaction Using Carboxylic Acids via N-(Acyloxy)phthalimides.

An improved, one-pot Minisci reaction has been developed using visible light, an organic photocatalyst, and carboxylic acids as radical precursors via the intermediacy of in situ-generated N-(acyloxy)phthalimides. The conditions employed are mild, demonstrate a high degree of functional group tolerance, and do not require a large excess of the carboxylic acid reactant. As a result, this reaction can be applied to drug-like scaffolds and molecules with sensitive functional groups, enabling late-stage functionalization, which is of high interest to medicinal chemistry.

Novel Conjugated Polymers Prepared by Direct (Hetero) arylation: An Eco-Friendly Tool for Organic Electronics.

The phthalimide (PhI) moiety has been attracting more attention as an excellent acceptor building block in donor-acceptor (D-A) conjugated polymers. In this paper; three D-A conjugated polymers with or without thiocarbonyl moieties are successfully prepared by the direct (hetero)-arylation polymerization (DHAP), which is an atom efficient and facile synthetic strategy to obtain polymer materials. Compared with the traditional carbon-carbon coupling reactions, this method possesses more advantages, including: fewer synthetic steps, avoidance of the preparation of the organometallic reagents, higher atom economy and fewer toxic byproducts, better compatibility with chemically sensitive functional groups and so on. All three of these designed PhI-based polymers exhibited favourable optoelectronic and thermal performance. The optical, thermodynamic and electrochemical properties of the synthesized polymers were systematically investigated using ultraviolet-visible (UV-vis) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and cyclic voltammetry (CV). The results of these three polymers indicated that thionation of the carbonyl was a highly effective methods to improve the properties of PhI-based polymers; and provided impetus for the development of thionated PhI derivatives for organic electronic applications.