Unprotected Anilines Research Articles

Copper‐Catalyzed Aerobic Benzylic C(sp3)−H Oxidation of Unprotected Aniline Derivatives for the Synthesis of Phenanthridines

AbstractHerein, we report a copper‐catalyzed intramolecular benzylic C(sp3)−H oxidation of unprotected aniline derivatives under aerobic conditions, which enables the preparation of phenanthridine compounds. To the best of our knowledge, this is the pioneering reaction of dehydrogenative C(sp3)−N bond formation from unprotected anilines under a Cu/O2 system. Notably, various anilines possessing alkyl, methoxy, halogen (fluoride, chloride, bromide, and iodide), trifluoromethyl, trifluoromethoxy, cyano, ester, and acetal groups can also participate in the reaction.

Cu-Mediated Tandem 2,3-Disubstituted Indole Synthesis from Simple Anilines and Internal Alkynes via C-H Annulation.

A simple, cost-effective, and straightforward method for the synthesis of 2,3-disubstituted indole scaffolds has been developed. The present protocol involves copper-mediated tandem hydroamination followed by C-H annulation of unprotected anilines with a wide range of internal alkynes. In the presence of Cu(OAc)2·H2O and trifluoroacetic acid (TFA), the reaction proceeds well to afford a variety of substituted indole derivatives in moderate to good yields. This process was found to be compatible with both primary and secondary anilines coupled with aromatic/aliphatic alkynes. High-purity copper nanoparticles can be recovered after the reaction, revealing the cost-effectiveness and environmentally benign feature of the current protocol.

Visible-Light-Mediated Ruthenium-Catalyzed para-Selective Alkylation of Unprotected Anilines

Anilines are important moieties in organic chemistry, pharmaceuticals, and materials science. Although para-selective functionalization of anilides and tertiary anilines is well established, unprotected anilines have posed a challenge. Herein, we report visible-light-mediated Ru(II)-catalyzed para-alkylation of anilines. The distinct Ru(II)–aniline complex enabled the reaction to proceed with extremely high efficiency (2 h) under mild conditions. The good functional group tolerance allowed late-stage functionalization and even aggregation-induced emission luminogen labeling of natural products and drugs. A mechanistic investigation suggests that the Ru(II)–aniline complex is crucial for both triggering the reaction and controlling the para-selectivity.

Palladium-Catalyzed Ortho C-H Arylation of Unprotected Anilines: Chemo- and Regioselectivity Enabled by the Cooperating Ligand [2,2'-Bipyridin]-6(1H)-one.

Metal-catalyzed C-H functionalizations on the aryl ring of anilines usually need cumbersome N-protection-deprotection strategies to ensure chemoselectivity. We describe here the Pd-catalyzed direct C-H arylation of unprotected anilines with no competition of the N-arylation product. The ligand [2,2'-bipyridin]-6(1H)-one drives the chemoselectivity by kinetic differentiation in the product-forming step, while playing a cooperating role in the C-H cleavage step. The latter is favored in an anionic intermediate where the NH moiety is deprotonated, driving the regioselectivity of the reaction toward ortho substitution.

Ligand- and Substrate-Controlled para C-H Borylation of Anilines at Room Temperature.

A new catalytic method for para borylation of unprotected anilines is described. The catalytic method is developed by designing a new type of ligand framework that enables para borylation at room temperature. We showed that whereas previously reported para borylation of 2-substituted anilines required multistep protection/deprotection sequences and a high reaction temperature, our method gives a straightforward solution for achieving para borylation without such protection/deprotection chemistry at room temperature.

Protecting-group-free ortho-C–H borylation of anilines enabled by mesoionic carbene-Ir complex

We describe an iridium-catalyzed ortho-selective C–H borylation of unprotected anilines. The employing strong σ-donating cyclometalated mesoionic carbene as C^C bidentate ligand is crucial for the high ortho-selectivity. Computational studies support outer-sphere X–H···Oboryl hydrogen bond interactions, which are strengthened by bidentate C^C ligand introduction. The method shows broad substrate scope and high functional group tolerance.

Friedel-Crafts Benzylation of Unprotected Anilines with Indole-3- carbinols to Access Trifluoro-methyl(indolyl)phenylmethanes

:An unprecedented protocol for the efficient and highly chemoselective alkylation of unprotected anilines with deactivated CF3-indole-3-carbinols promoted by In(OTf)3 has been developed. A series of diversified trifluoromethylated (indolyl)phenylmethanes were produced featuring the C-alkylation in moderate to high chemical yields and with high regioselectivities.

Exploration of a Nitromethane-Carbonylation Strategy during Route Design of an Atropisomeric KRASG12C Inhibitor.

Route design and proof of concept synthesis was conducted on a synthetically challenging atropisomeric KRASG12C inhibitor to support clinical API manufacture. Improvements to the synthesis of a chiral piperazine fragment gave reduced step count and streamlined protecting group strategy via the formation and methanol ring opening of an N-carboxy-anhydride (NCA). The complex atropisomeric nitroquinoline was accessed via an early stage salt-resolution followed by a formal two-part nitromethane-carbonylation, avoiding a high temperature Gould-Jacobs cyclization that previously led to atropisomer racemization. The substrate scope of the formal nitromethane-carbonylation strategy was further explored for a range of ortho-substituted bromo/iodo unprotected anilines.

Iodine/DMSO-Promoted Selective Direct Arylthiation of Anilines with Thiols under Metal-Free Conditions.

An iodine-promoted divergent thiolation of unprotected anilines with thiols for the synthesis of sulfide anilines has been described. The combinational use of I2 and DMSO played an important role to realize this kind of transformation without the aid of a metal catalyst and strong oxidants. The reaction selectivity was well controlled to provide mono-, bis-, and trisubstituted diaryl sulfide derivatives. More importantly, iodination and sulfenylation can occur simultaneously to provide useful multifunctionalized iodoaniline products. This method afforded an efficient protocol for the construct C-S and C-I bonds from the C-H bond under mild reaction conditions.

Catalyst-Controlled Regioselective Chlorination of Phenols and Anilines through a Lewis Basic Selenoether Catalyst.

We report a highly efficient ortho-selective electrophilic chlorination of phenols utilizing a Lewis basic selenoether catalyst. The selenoether catalyst resulted in comparable selectivities to our previously reported bis-thiourea ortho-selective catalyst, with a catalyst loading as low as 1%. The new catalytic system also allowed us to extend this chemistry to obtain excellent ortho-selectivities for unprotected anilines. The selectivities of this reaction are up to >20:1 ortho/para, while the innate selectivities for phenols and anilines are approximately 1:4 ortho/para. A series of preliminary studies revealed that the substrates require a hydrogen-bonding moiety for selectivity.

On the Superior Activity of In(I) versus In(III) Cations Toward ortho-C-Alkylation of Anilines and Intramolecular Hydroamination of Alkenes.

An efficient ortho-C-alkylation of unprotected anilines with a variety of styrenes and alkenes using a univalent cationic indium(I) catalyst is reported. Mechanistic studies revealed that the reaction likely proceeds via a tandem hydroamination/Hofmann-Martius rearrangement. The high compatibility between the cationic indium(I) complex and primary anilines led us to develop an In(I)+-catalyzed hydroamination of alkenes using unprotected primary and secondary alkenylamines. Computations support the catalytic activity of naked In(I)+ ions, with an outer sphere mechanism for the C-N bond formation and a potentially inner sphere protodemetallation.

Tf2O-mediated Reaction of Alkenyl Sulfoxides with Unprotected Anilines in Flow Microreactors

Flow microreactors have allowed an efficient extended Pummerer reaction of ketene dithioacetal monoxides with anilines by precise control of unstable sulfonium intermediates and spatial separation ...

Aromatic C-H amination in hexafluoroisopropanol.

We report a direct radical aromatic amination reaction that provides unprotected anilines with an improvement in the substrate scope compared to prior art. Hydrogen bonding by the solvent hexafluoroisopropanol to anions of cationic species is responsible for increased reactivity and can rationalize the enhancement in substrate scope. Our findings may have bearings on radical additions to arenes for direct C-H functionalization in general.

Iodine mediated oxidative cross-coupling of unprotected anilines and heteroarylation of benzothiazoles with 2-methylquinoline

Iodine-promoted oxidative C-H/C-H cross-coupling of unprotected anilines and 2-methylquinoline to furnish C4-carbonylated aniline (4-aminophenyl)(quinoline-2-yl) methanones in moderate to good yields has been demonstrated. This work provides the first site-selective approach for the synthesis of free amino groups containing methanones including unprecedented C-H functionalization rather than the N-H functionalization of unprotected anilines via the Kornblum oxidation of 2-methylquinoline. Furthermore, we noticed that the incorporation of KOH under standard conditions provides 2-heteroarylbenzothiazoles from benzothiazoles and 2-methylquinoline in good to excellent yields. These transformations do not require any transition metals or peroxides and tolerate various functional groups such as methoxy, hydroxy, bromo, chloro and nitro groups. Moreover, a plausible mechanistic pathway is proposed.

Coupling N-H Deprotonation, C-H Activation, and Oxidation: Metal-Free C(sp3)-H Aminations with Unprotected Anilines.

An intramolecular oxidative C(sp3)-H amination from unprotected anilines and C(sp3)-H bonds readily occurs under mild conditions using t-BuOK, molecular oxygen and N,N-dimethylformamide (DMF). Success of this process, which requires mildly acidic N-H bonds and an activated C(sp3)-H bond (BDE < 85 kcal/mol), stems from synergy between basic, radical, and oxidizing species working together to promote a coordinated sequence of deprotonation: H atom transfer and oxidation that forges a new C-N bond. This process is applicable for the synthesis of a wide variety of N-heterocycles, ranging from small molecules to extended aromatics without the need for transition metals or strong oxidants. Computational results reveal the mechanistic details and energy landscape for the sequence of individual steps that comprise this reaction cascade. The importance of base in this process stems from the much greater acidity of transition state and product for the 2c,3e C-N bond formation relative to the reactant. In this scenario, selective deprotonation provides the driving force for the process.

Convenient Access to C4‐Dicarbonylation of Anilines by Iodine‐Promoted Oxidative Cross‐Coupling Reactions

AbstractAn innovative route for the construction of C4‐dicarbonylation of anilines from simple and readily available anilines and phenyl acetylene has been developed. The iodine‐promoted oxidative cross‐coupling reaction performed well and the highlight of this protocol was not N−H functionalization but C−H functionalization of unprotected anilines.

Supramolecular Ensemble of Tetraphenylcyclopentadienone Derivative and HgO nanoparticles: A One-Pot Approach for the Synthesis of Quinoline and Quinolone Derivatives

Electron deficient tetraphenylcyclopentadienone appended with thiophene has been designed and synthesized which exihibits aggregation induced emission enhancement (AIEE) to form fluorescent assemblies in aqueous media. These emissive aggregates exhibit mercury induced emission enhancement in aqueous media and serve as reactors for the generation of mercury oxide nanoparticles. Further, the in situ generated supramolecular ensemble of tetraphenylcyclopentadienone aggregates and HgO nanomaterial show high catalytic efficiency in the reactions for the synthesis of N-heterocyclic derivatives through ortho C−H functionalization of unprotected anilines. In addition, this catalytic system has been utilized for the kynurenic acid methyl esters (KYNA methyl ester) derivatives based non-steroidal anti-inflammatory drug through C−H functionalization strategy which is unprecedented in the literature

Metal-free oxidative para-acylation of unprotected anilines with N-heteroarylmethanes.

A selective oxidative para-acylation of unprotected anilines with methyl groups in N-heteroarylmethanes was achieved. This transformation proceeds under mild metal-free reaction conditions to produce the corresponding valuable diarylmethanones in good to high yields, featuring high site-selectivity, high functional-group-tolerance, gram-scale synthesis and easy product-derivation. Preliminary mechanistic studies revealed that the present oxidative para-acylation would take place via a Friedel-Crafts-type process of in situ imines and the steric hindrance might be the key issue for the high regio-selectivity.

ChemInform Abstract: Iodine‐Promoted Oxidative Cross‐Coupling of Unprotected Anilines with Methyl Ketones: A Site‐Selective Direct C—H Bond Functionalization to C4‐Dicarbonylation of Anilines.

An unprecedented direct dual C–H bond functionalization of unprotected anilines and methyl ketones has been demonstrated. It is the first example of iodine-promoted highly chemo- and site-selective oxidative C–H/C–H cross-coupling of anilines and methyl ketones to furnish the C4-dicarbonylation of anilines in moderate to good yields. Moreover, coproduct HI acted as a catalyst in the reaction. The salient feature of this approach is unprecedented C–H functionalization rather than N–H functionalization of unprotected anilines.

Iodine-Promoted Oxidative Cross-Coupling of Unprotected Anilines with Methyl Ketones: A Site-Selective Direct C–H Bond Functionalization to C4-Dicarbonylation of Anilines

An unprecedented direct dual C-H bond functionalization of unprotected anilines and methyl ketones has been demonstrated. It is the first example of iodine-promoted highly chemo- and site-selective oxidative C-H/C-H cross-coupling of anilines and methyl ketones to furnish the C4-dicarbonylation of anilines in moderate to good yields. Moreover, coproduct HI acted as a catalyst in the reaction. The salient feature of this approach is unprecedented C-H functionalization rather than N-H functionalization of unprotected anilines.