Copper-Catalyzed Alkene Diamination: Synthesis of Chiral 2-Aminomethyl Indolines and Pyrrolidines

Catalytic asymmetric synthesis of 1,2-diamines

The asymmetric catalytic synthesis of 1,2-diamines has received considerable interest, especially in the last ten years, due to their presence in biologically active compounds and their applications for the development of synthetic building blocks, chiral ligands and organocatalysts. Synthetic strategies based on C-N bond-forming reactions involve mainly (a) ring opening of aziridines and azabenzonorbornadienes, (b) hydroamination of allylic amines, (c) hydroamination of enamines and (d) diamination of olefins. In the case of C-C bond-forming reactions are included (a) the aza-Mannich reaction of imino esters, imino nitriles, azlactones, isocyano acetates, and isothiocyanates with imines, (b) the aza-Henry reaction of nitroalkanes with imines, (c) imine-imine coupling reactions, and (d) reductive coupling of enamines with imines, and (e) [3+2] cycloaddition with imines. C-H bond forming reactions include hydrogenation of CN bonds and C-H amination reactions. Other catalytic methods include desymmetrization reactions of meso-diamines.

Cobalt-catalyzed amination of aziridines and azetidines toward 1,2- and 1,3-diamines

Diamines play important roles in synthetic organic chemistry and thus facilitate life and materials sciences. Herein we report a cobalt-catalyzed ring opening, nucleophilic amination of aziridines and azetidines with N-fluorosulfonamides toward a wide range of 1,2- and 1,3-diamine derivatives in moderate to good yields under mild conditions.

Transition-Metal-Catalyzed 1,2-Diaminations of Olefins: Synthetic Methodologies and Mechanistic Studies

1,2-Diamines are synthetically important motifs in organo-catalysis, natural products, and drug research. Continuous utilization of transition-metal based catalyst in direct 1,2-diamination of olefines, in contrast to metal-free transformations, with numerous impressive advances made in recent years (2015-2023). This review summarized contemporary research on the transition-metal catalyzed/mediated [e. g., Cu(II), Pd(II), Fe(II), Rh(III), Ir(III), and Co(II)] 1,2-diamination (asymmetric and non-asymmetric) especially emphasizing the recent synthetic methodologies and mechanistic understandings. Moreover, up-to-date discussion on (i) paramount role of oxidant and catalyst (ii) key achievements (iii) generality and uniqueness, (iv) synthetic limitations or future challenges, and (v) future opportunities are summarized related to this potential area.

1,2-Diamination of Alkenes via 1,3-Dipolar Cycloaddition with Azidium Ions or Azides

We describe two new methods for the 1,2-diamination of alkenes. First, either an azidium ion (ArN═N⁺═NAr) undergoes 1,3-dipolar cycloaddition with an alkene to give a 1,2,3-triazolinium ion directly, or an intramolecular azide-alkene cycloaddition followed by N-benzylation provides the same. Second, hydrogenation of the 1,2,3-triazolinium ion over Raney Ni excises the central N atom and gives the 1,2-diamine. The stereochemistry of the alkene is usually, but not always, preserved in the 1,2-diamine.

NIS-Promoted Selective Amino-Diazidation and Amino-Iodoazidation of O-Homoallyl Benzimidates: Synthesis of Vicinal Diazido 1,3-Oxazines and Vicinal Iodoazido 1,3-Oxazines

Amines, especially those with multi-nitrogen moieties, are widespread in natural products and biologically active compounds. Thus, the development of direct and efficient methods to introduce multiple nitrogen-containing fragments into compounds in one step is highly desirable yet challenging. Herein, we report an NIS-promoted selective amino-diazidation and amino-iodoazidation of O-homoallyl benzimidates with NaN₃. By using this protocol, a variety of vicinal diazido-substituted 1,3-oxazines and vicinal iodoazido-substituted 1,3-oxazines were directly synthesized in a controllable manner. Preliminary mechanistic investigations revealed that the reaction operates through a NIS-promoted four-step cascade process. The developed method has the merits of metal-free, excellent functional group compatibility, simple operation, and mild conditions.

Nitrogen-Centered Radicals in Functionalization of sp2 Systems: Generation, Reactivity, and Applications in Synthesis

The chemistry of nitrogen-centered radicals (NCRs) has plentiful applications in organic synthesis, and they continue to expand as our understanding of these reactive species increases. The utility of these reactive intermediates is demonstrated in the recent advances in C-H amination and the (di)amination of alkenes. Synthesis of previously challenging structures can be achieved by efficient functionalization of sp² moieties without prefunctionalization, allowing for faster and more streamlined synthesis. This Review addresses the generation, reactivity, and application of NCRs, including, but not limited to, iminyl, aminyl, amidyl, and aminium species. Contributions from early discovery up to the most recent examples have been highlighted, covering radical initiation, thermolysis, photolysis, and, more recently, photoredox catalysis. Radical-mediated intermolecular amination of (hetero)arenes can occur with a variety of complex amine precursors, generating aniline derivatives, an important class of structures for drug discovery and development. Functionalization of olefins is achievable in high anti-Markovnikov regioselectivity and allows access to difunctionalized structures when the intermediate carbon radicals are trapped. Additionally, the reactivity of NCRs can be harnessed for the rapid construction of N-heterocycles such as pyrrolidines, phenanthridines, quinoxalines, and quinazolinones.

A practical and cost-effective approach to polysubstituted pyrimidine derivatives via DBU mediated redox isomerization of propargyl alcohol and subsequent N-C-N fragment condensation

A straightforward, efficient yet effortless approach for the synthesis of structurally important triarylated pyrimidine derivatives has been successfully developed using secondary propargyl alcohol and commercially available amidines under mild basic...

Catalytic Diastereo- and Enantioconvergent Synthesis of Vicinal Diamines from Diols through Borrowing Hydrogen

We present herein an unprecedented diastereoconvergent synthesis of vicinal diamines from diols through an economical, redox-neutral process. Under cooperative ruthenium and Lewis acid catalysis, readily available anilines and 1,2-diols (as a mixture of diastereomers) couple to forge two C-N bonds in an efficient and diastereoselective fashion. By identifying an effective chiral iridium/phosphoric acid co-catalyzed procedure, the first enantioconvergent double amination of racemic 1,2-diols has also been achieved, resulting in a practical access to highly valuable enantioenriched vicinal diamines.

Copper-Catalyzed Diamination of Unactivated Alkenes With Electron-Rich Amino Sources

The catalytic intermolecular diamination of unactivated alkenes with electron-rich amino sources is a challenge. Herein, by employing a directing-group strategy, a copper-catalyzed diamination of unactivated alkenes was realized. Symmetrical diamines were efficiently produced in a highly diastereoselective manner with readily available dialkylamines as amino sources, while a one-pot and two-step operation was necessary to produce the unsymmetrical diamines. These reactions were proposed to proceed through aziridinium intermediates.

Regioselective Three-Component Synthesis of Vicinal Diamines via 1,2-Diamination of Styrenes

The vicinal diamine motif plays a significant role in natural products, drug design, and organic synthesis, and development of synthetic methods for the synthesis of diamines is a long-standing interest. Herein, we report a regioselective intermolecular three-component vicinal diamination of styrenes with acetonitrile and azodicarboxylates. The diamination products can be produced in moderate to excellent yields via the Ritter reaction. Synthetic applications and theoretical studies of this reaction have been conducted.

Access to Chiral Diamine Derivatives through Stereoselective Cu-Catalyzed Reductive Coupling of Imines and Allenamides

Chiral 1,2-diamino compounds are important building blocks in organic chemistry for biological applications and as asymmetric inducers in stereoselective synthesis that are challenging to prepare in a straightforward and stereoselective manner. Herein, we disclose a cost-effective and readily available Cu-catalyzed system for the reductive coupling of a chiral allenamide with N-alkyl substituted aldimines to access chiral 1,2-diamino synthons as single stereoisomers in high yields. The method shows broad reaction scope and high diastereoselectivity and can be easily scaled using standard Schlenk techniques. Mechanistic investigations by density functional theory calculations identified the mechanism and origin of stereoselectivity. In particular, the addition to the imine was shown to be reversible, which has implications toward development of catalyst-controlled stereoselective variants of the identified reductive coupling of imines and allenamides.

Highly diastereoselective synthesis of vicinal diamines via a Rh-catalyzed three-component reaction of diazo compounds with diarylmethanimines and ketimines

A Rh-catalyzed selective three-component reaction of diazo compounds with diarylmethanimines and ketimines is reported that offers an efficient and convenient access to vicinal diamine derivatives with two tertiary stereocenters in high yields.

Enantioselective, Aerobic Copper-Catalyzed Intramolecular Carboamination and Carboetherification of Unactivated Alkenes

Reduction of waste is an important goal of modern organic synthesis. We report herein oxidase reactivity for enantioselective intramolecular copper-catalyzed alkene carboamination and carboetherification reactions where previously used stoichiometric MnO2 has been replaced with oxygen. This substitution was risky as the reaction mechanism is thought to involve C-C bond formation via addition of alkyl carbon radicals to arenes. Such intermediates are also susceptible to C-O bond formation via O2 addition. Control of absolute stereochemistry under aerobic conditions was also uncertain. The oxidative cyclization efficiencies appear to track with the ease of the radical addition to the arenes.

Recent advances in copper-catalysed radical-involved asymmetric 1,2-difunctionalization of alkenes

This tutorial review highlights the recent progress in copper-catalysed radical asymmetric 1,2-difunctionalization of alkenes.

Rhodium(iii)-catalyzed diamidation of olefins via amidorhodation and further amidation

Rh(iii)/Co(iii)-catalyzed diamidation of amide-tethered olefins has been realized using dioxazolones and arylsulfonamides as different classes of amidating reagents.

Catalytic, Enantioselective syn-Diamination of Alkenes

The enantioselective, vicinal diamination of alkenes represents one of the stereocontrolled additions that remains an outstanding challenge in organic synthesis. A general solution to this problem would enable the efficient and selective preparation of widely useful, enantioenriched diamines for applications in medicinal chemistry and catalysis. In this article, we describe the first enantioselective, syn-diamination of simple alkenes mediated by a chiral, enantioenriched organoselenium catalyst together with a N,N'-bistosyl urea as the bifunctional nucleophile and N-fluorocollidinium tetrafluoroborate as the stoichiometric oxidant. Diaryl, aryl-alkyl, and alkyl-alkyl olefins bearing a variety of substituents are all diaminated in consistently high enantioselectivities but variable yields. The reaction likely proceeds through a Se(II)/Se(IV) redox catalytic cycle reminiscent of the syn-dichlorination reported previously. Furthermore, the syn-stereospecificity of the transformation shows promise for highly enantioselective diaminations of alkenes with no strong steric or electronic bias.

Regio- and Enantioselective Synthesis of 1,2-Diamine Derivatives by Copper-Catalyzed Hydroamination

A highly regio- and enantioselective synthesis of 1,2-diamine derivatives from γ-substituted allylic pivalamides using copper-catalyzed hydroamination is reported. The N-pivaloyl group is essential, in both facilitating the hydrocupration step and suppressing an unproductive β-elimination from the alkylcopper intermediate. This approach enables an efficient construction of chiral differentially protected vicinal diamines under mild conditions with broad functional group tolerance.

Iodine-promoted Intermolecular Dehydrogenation Diamination: Synthesis of Unsymmetrical α,β-Diamido Ketones

Iodine-promoted direct diamination of α,β-unsaturated ketone to form two C-N bonds has been developed starting from chalcone and secondary amine. This reaction was performed in THF at 50 °C in the presence of I₂ and K₂ CO_3. The protocol is metal-free, operationally simple and carried out under mild conditions, providing an effective new way for directing diamination reactions.

Synthesis of Sulfonylated Lactams by Copper-Mediated Aminosulfonylation of 2-Vinylbenzamides with Sodium Sulfinates

Treatment of 2-vinylbenzamide derivatives with sulfinate sodium in the presence of Cu(NO₃)₂·3H₂O led to an intra/intermolecular aminosulfonylation reaction to produce sulfonylated lactams in moderate to good yields. The developed method features the easily available and stable sulfone reagents, ease of operation, and a broad functional group tolerance.

Catalyst-free amination of α-cyanoarylacetates enabled by single-electron transfer

A radical benzylic amination of α-cyanoarylacetates without the assistance of any transition-metal catalysts or external photosensitizers was realized.

Aminative Umpolung cyclization for synthesis of chiral exocyclic vicinal diamines

Chiral exocylic vicinal diamines are biologically and chemically important compounds, but they are not easy to make. In this paper, an interesting aminative Umpolung cyclization process has been developed. Aromatic aldehydes 6 bearing an electrophilic chiral sulfinimine group underwent imine formation with 2,2-diphenylglycine (2), decarboxylation, and subsequent Umpolung cyclization, producing various trans-diamines 10 in 84-96% yields with high trans/cis ratios under very mild conditions. This work not only provides an efficient, clean, and mild method for the synthesis of chiral exocyclic vicinal diamines in one step but also represents a new application of aminative Umpolung strategy on intramolecular reactions.

Enantioselective Synthesis of anti-1,2-Diamines by Cu-Catalyzed Reductive Couplings of Azadienes with Aldimines and Ketimines

Here we report highly efficient and chemoselective azadiene-imine reductive couplings catalyzed by (Ph-BPE)Cu-H that afford anti-1,2-diamines. In all cases, reactions take place with either aldimine or ketimine electrophiles to deliver a single diastereomer of product in >95:5 er. The products' diamines are easily differentiable, facilitating downstream synthesis.

Asymmetric Aza-Wacker-Type Cyclization of N-Ts Hydrazine-Tethered Tetrasubstituted Olefins: Synthesis of Pyrazolines Bearing One Quaternary or Two Vicinal Stereocenters

We have developed an asymmetric aza-Wacker-type cyclization of N-Ts hydrazine-tethered tetrasubstituted olefins, affording optically active pyrazolines bearing chiral tetrasubstituted carbon stereocenters. This reaction is tolerant to a broad range of substrates under mild reaction conditions, giving the desired chiral products with high enantioselectivities. Generation of two vicinal stereocenters on the C═C double bonds was also achieved with high selectivities, a process which has been rarely studied for Wacker-type reactions. A mechanistic study revealed that this aza-Wacker-type cyclization undergoes a syn-aminopalladation process. It was also found that for substrates bearing two linear alkyl substituents on the outer carbon atom of the olefin, both of which are larger than a methyl group, the alkyl substituent that is cis to the intranucleophilic group participates more readily in β-hydride elimination. When one of the two alkyl substituents on the outer carbon atom of the olefin is a methyl group, β-hydride elimination proceeds selectively at the methylene side, thus both diastereomers can be prepared via switching the configuration of the olefin. Furthermore, the product can be converted to a pharmaceutical compound in high yields over three steps.

Pd(II)-Catalyzed Asymmetric Oxidative 1,2-Diamination of Conjugated Dienes with Ureas

A palladium(II)-catalyzed asymmetric 1,2-diamination of 1,3-dienes with readily available dialkylureas was established by using a chiral pyridine-oxazoline ligand. The diamination reaction exclusively occurs at the terminal C-C double bond of the 1,3-dienes to give 4-vinylimidazolidin-2-ones in high yields and with excellent levels of enantioselectivity (up to 99% yield, 97% ee). The reaction could feasibly be applied for gram-scale synthesis with a 1:1 ratio of the diene and the urea.

Diethylzinc-Mediated Metalloamination-Alkylation of N, N-Dimethylhydrazinoalkenes. Catalysis of C-Zn Alkylation Using Simple Cu(I) Salts

Metalloamination-alkylation of representative N,N-dimethyl-hydrazinoalkenes has been shown to be effectively catalyzed by CuBr-SMe₂, CuCN, and Cul. The current method obviates the use of stoichiometric CuCN(LiCl)₂ as a promoter for the electrophilic functionalization event.

Copper-mediated intramolecular aminofluorination of 1,3-dienes by using nucleophilic fluorine reagents

A copper-mediated intramolecular aminofluorination of 1,3-dienes is disclosed, in which both AgF and Et₃N·3HF can be used as the fluorine source.

Copper-catalyzed aminoalkynylation of alkenes with hypervalent iodine reagents

A copper-catalyzed aminoalkynylation of alkenes is achieved with ethynylbenziodoxolone (EBX) reagents under mild conditions with only 1 mol% copper catalyst. This transformation allows for rapid construction of diverse important azahetereocycles and installation of valuable alkyne groups in one step. The developed method features remarkable substrate scope for both terminal and internal alkenes as well as different alkynyl groups, presenting great potential for broad applications in synthesis, bioconjugation, and molecular imaging.

Copper-Catalyzed Ligand-Free Diazidation of Olefins with TMSN3 in CH3CN or in H2O

An environmentally benign, copper-catalyzed diazidation of a broad range of olefins, including vinylarenes, unactivated alkenes, allene, and dienes, under mild conditions with TMSN₃ (trimethylazidosilane) as azido source, has been developed. This reaction can be carried out in organic solvent or in aqueous solution where water is the sole solvent. The functional group compatibility of this reaction is good, which is proved by late-stage functionalizations of complex substrates.