Oxidative Three-Component Carboamination of Vinylarenes with Alkylboronic Acids

Cu-Catalyzed Three-Component Alkene Carboamination: Mechanistic Insights and Rational Design to Overcome Limitations

Herein, we report mechanistic investigations into the Cu-catalyzed three-component carboamination of alkenes with α-halo carbonyls and aryl amines via an oxocarbenium intermediate. Monitoring the reaction reveals the formation of transient atom transfer radical addition (ATRA) intermediates with both electron-neutral and deficient vinyl arenes as well as unactivated alkenes. Based on our experimental studies and density functional theory calculations, the oxocarbenium is generated through atom transfer and subsequent intramolecular substitution. Further, mechanistic factors that dictate the regioselectivity of the nucleophilic attack onto the oxocarbenium to afford the γ-amino ester, γ-iminolactone, or γ-lactone are discussed. A strategy to overcome scope limitation with respect to unactivated alkenes is developed using the mechanistic insights gained herein. Finally, we demonstrate that under modified conditions, our Cu catalyst enables the ATRA reaction between a variety of alkyl halides and vinyl arenes/α-olefins, and we present a one-pot, two-step carbofunctionalization with an array of nucleophiles through ATRA/SN2.

Copper-Catalyzed Three-Component 1,5-Carboamination of Vinylcyclopropanes

The 1,5-copper-catalyzed carboamination of vinylcyclopropanes is presented. A carbon-centered radical, formed upon reduction of an alkyl halide by Cu(I), adds across the alkene of a vinylcyclopropane, triggering ring opening to generate a benzylic radical, which, finally, undergoes copper-mediated amination to afford a homoallylic amine. The reaction occurs with outstanding regio- and good to very good diastereoselectivities. The scope of the reaction is demonstrated with respect to all three components: alkyl halide, vinylcyclopropane, and amine nucleophile. A total of 38 examples are presented with an average yield of 60%.

Cooperative Photoredox and N-Heterocyclic Carbene Catalysis Suzuki-Miyaura-Type Reaction: Radical Coupling of Aroyl Fluorides and Alkyl Boronic Acids

An intermolecular Suzuki-Miyaura-type reaction of benzoyl fluorides with alkyl boronic acids to synthetic ketone was revealed by cooperative N-heterocyclic carbene (NHC) and photoredox catalysis. Various alkyl boric acids can be converted into alkyl radicals without external oxidants or activators. Moreover, the catalytic system was feasible for the difunctionalization of styrenes via a radical relay process. Mechanistic experiments suggested that the benzoate anion intermediate might play a unique role in this reaction system.

Photoexcitation of (diarylmethylene)amino benziodoxolones for alkylamination of styrene derivatives with carboxylic acids

The alkylamination of alkenes using pristine carboxylic acids was achieved by the photoexcitation of (diarylmethylene)amino benziodoxolones (DABXs), which serve as both an oxidant and an aminating reagent (an iminyl radical precursor). The developed method is a simple photochemical reaction without the need for external photosensitizers and shows a broad substrate scope for aliphatic carboxylic acids leading to the formation of primary, secondary, and tertiary alkyl radicals, thus enabling the facile synthesis of various structurally complex amines. Mechanistic investigations including transient absorption spectroscopy measurements using a laser flash photolysis (LFP) method disclosed the unique photochemical reactivity of DABXs, which undergoes homolysis of their I-N bonds to give an iminyl radical and ortho-iodobenzoyloxy radical, the latter of which participates in the single-electron oxidation of carboxylates.

Ligand-Enabled Carboamidation of Unactivated Alkenes through Enhanced Organonickel Electrophilicity

Catalytic carboamination of alkenes is a powerful synthetic tool to access valuable amine scaffolds from abundant and readily available alkenes. Although a number of synthetic approaches have been developed to achieve the rapid buildup of molecular complexity in this realm, the installation of diverse carbon and nitrogen functionalities onto unactivated alkenes remains underdeveloped. Here we present a ligand design approach to enable nickel-catalyzed three-component carboamidation that is applicable to a wide range of alkenyl amine derivatives via a tandem process involving alkyl migratory insertion and inner-sphere metal-nitrenoid transfer. With this method, various nitrogen functionalities can be installed into both internal and terminal unactivated alkenes, leading to differentially substituted diamines that would otherwise be difficult to access. Mechanistic investigations reveal that the tailored Ni(cod)(BQiPr) precatalyst modulates the electronic properties of the presumed π-alkene-nickel intermediate via the quinone ligand, leading to enhanced carbonickelation efficiency across the unactivated C═C bond. These findings establish nickel's ability to catalyze multicomponent carboamidation with a high efficiency and exquisite selectivity.

Trinuclear Gold-Catalyzed 1,2-Difunctionalization of Alkenes

Activated alkyl halides have been extensively explored to generate alkyl radicals with Ru- and Ir- photocatalysts for 1,2-difunctionalization of alkenes, but unactivated alkyl bromides remain challenging substrates due to their strong reduction potential. Here we report a three-component 1,2-difunctionalization reaction of alkenes, unactivated alkyl bromides and nucleophiles (e.g., amines and indoles) using a trinuclear gold catalyst [Au3 (tppm)2 ](OTf)3 . It can achieve the 1,2-aminoalkylation and 1,2-alkylarylation readily. This protocol has a broad reaction scope and excellent functional group compatibility (>100 examples with up to 96 % yield). It also affords a robust formal [2+2+1] cyclization strategy for the concise construction of pyrrolidine skeletons under mild reaction conditions. Mechanistic studies support an inner-sphere single electron transfer pathway for the successful cleavage of inert C-Br bonds.

Cu-Catalyzed Three-Component Carboamination of Electron Deficient Olefins

The copper-catalyzed three-component carboamination of atropates for the synthesis of α-aryl amino acid derivatives is presented. The scope of the reaction is explored with respect to all three coupling partners: the alkyl halide, the atropate, and the aryl amine. A total of 41 examples are included, with yields of ≤92%. Both primary and secondary aryl amines participate in the carboamination along with α-haloesters, nitriles, and perfluoroiodoalkanes. Mechanistic investigations support a radical mechanism involving Cu-mediated C-N bond formation with the radical adduct.

Cu-Catalyzed Polychloromethylamination of Styrenes through C(sp3 )-H Bond Cleavage

A copper-catalyzed three-component coupling reaction has been developed allowing the rapid building of valuable complex highly functionalized β-polychloromethyl amines from simple styrenes, arylamines, and dichloromethane/chloroform. Using aryldiazonium salts as a radical initiator, a series of corresponding products are obtained with moderate to good yields under a carbon dioxide or nitrogen atmosphere (50 psi). In addition, good functional group tolerance can be observed.

A Counterion/Ligand-Tuned Chemo- and Enantioselective Copper-Catalyzed Intermolecular Radical 1,2-Carboamination of Alkenes

The copper-catalyzed enantioselective intermolecular radical 1,2-carboamination of alkenes with readily accessible alkyl halides is an appealing strategy for producing chiral amine scaffolds. The challenge arises from the easily occurring atom transfer radical addition between alkyl halides and alkenes and the issue of enantiocontrol. We herein describe a radical alkene 1,2-carboamination with sulfoximines in a highly chemo- and enantioselective manner. The key to the success of this process is the conceptual design of a counterion/highly sterically demanded ligand coeffect to promote the ligand exchange of copper(I) with sulfoximines and forge chiral C-N bonds between alkyl radicals and the chiral copper(II) complex. The reaction covers alkenes bearing distinct electronic properties, such as aryl-, heteroaryl-, carbonyl-, and aminocarbonyl-substituted ones, and various radical precursors, including alkyl chlorides, bromides, iodides, and the CF₃ source. Facile transformations deliver many chiral amine building blocks of interest in organic synthesis and related areas.

Rh(III)-Catalyzed chemo-, regio- and stereoselective carboamination of sulfonyl allenes with N-phenoxy amides or N-enoxy imides

The Rh(III)-catalyzed chemo-, regio- and stereoselective carboamination of sulfonyl allenes has been realized by virtue of either N-phenoxy amides or N-enoxy imides simultaneously acting as the C- and N-sources, via redox-neutral tandem C-H activation/allene insertion/oxidative addition/C-N bond formation for the direct construction of allylamine derivatives equipped with an α-quaternary carbon center. This protocol features high atom-economy with good substrate compatibility and exhibits profound synthetic potential for late-stage C-H modification of complex molecules.

Advances in free-radical alkylation and arylation with organoboronic acids

Organoboronic acids act as carbon-centered radical precursors that are widely utilized to construct diverse C-C bonds. This review summarizes the advances in this field. The content is divided into four parts according to the different categories of coupling partners with organoboronic acids. The reaction conditions as well as the mechanisms are demonstrated in each part.

Divergent Aminocarbonylations of Alkynes Enabled by Photoredox/Nickel Dual Catalysis

A metallaphotoredox-catalyzed strategy for the selective and divergent aminocarbonylation of alkynes with amines and 1 atm of CO is reported. This synergistic protocol not only enables the Markovnikov-selective hydroaminocarbonylation of alkynes to afford α,β-unsaturated amides, but also facilitates a sequential four-component hydroaminocarbonylation/radical alkylation in the presence of tertiary and secondary alkyl boronate esters, which allows for straightforward conversion of alkynes into corresponding amides. Preliminary mechanistic studies disclose that a photoinduced oxidative insertion of aniline and CO into nickel followed by a migratory insertion of (carbamoyl)nickel species could be involved.

Three-component 1,2-carboamination of vinyl boronic esters via amidyl radical induced 1,2-migration

Three-component 1,2-carboamination of vinyl boronic esters with alkyl/aryl lithium reagents and N-chloro-carbamates/carboxamides is presented. Vinylboron ate complexes generated in situ from the boronic ester and an organo lithium reagent are shown to react with readily available N-chloro-carbamates/carboxamides to give valuable 1,2-aminoboronic esters. These cascades proceed in the absence of any catalyst upon simple visible light irradiation. Amidyl radicals add to the vinylboron ate complexes followed by oxidation and 1,2-alkyl/aryl migration from boron to carbon to give the corresponding carboamination products. These practical cascades show high functional group tolerance and accordingly exhibit broad substrate scope. Gram-scale reaction and diverse follow-up transformations convincingly demonstrate the synthetic potential of this method.

Nickel-Catalyzed 1,2-Carboamination of Alkenyl Alcohols

An alcohol-directed, nickel-catalyzed three-component umpolung carboamination of unactivated alkenes with aryl/alkenylboronic esters and electrophilic aminating reagents is reported. This transformation is enabled by specifically tailored O-(2,6-dimethoxybenzoyl)hydroxylamine electrophiles that suppress competitive processes, including undesired β-hydride elimination and transesterification between the alcohol substrate and electrophile. The reaction delivers the desired 1,2-carboaminated products with generally high regio- and syn-diastereoselectivity and exhibits a broad scope of coupling partners and alkenes, including complex natural products. Various mechanistic experiments and analysis of the stereochemical outcome with a cyclic alkene substrate, as confirmed by X-ray crystallographic analysis, support alcohol-directed syn-insertion of an organonickel(I) species.

Rh(III)-Catalyzed Three-Component Syn-Carboamination of Alkenes Using Arylboronic Acids and Dioxazolones

Herein we report a Rh(III)-catalyzed three-component carboamination of alkenes from readily available aryl boronic acids as a carbon source and dioxazolones as nitrogen electrophiles. This protocol provides facile access to valuable amine products including α-amino acid derivatives in good yield and regioselectivity without the need for a directing functionality. A series of experiments suggest a mechanism in which the Rh(III) catalyst undergoes transmetalation with the aryl boronic acid followed by turnover limiting, alkene migratory insertion into the Rh(III)-aryl bond. Subsequently, fast Rh-nitrene formation provides the syn-carboamination product selectively after reductive elimination and proto-demetalation. Importantly, the protocol provides 3-component coupling products in preference to a variety of 2-component undesired by-products.

Three-component photoredox 1,2-alkylamination of styrenes with alkanes and nitrogen nucleophiles via C(sp3)–H bond cleavage

A three-component photoredox 1,2-alkylamination of styrenes involving functionalization of C(sp3)–H bonds in alkyl halides instead of functionalization of C-halogen bonds is disclosed.