anti‐Markovnikov Hydroamination of Alkenes Catalyzed by a Two‐Component Organic Photoredox System: Direct Access to Phenethylamine Derivatives

Disclosed herein is a general catalytic system for the intermolecular anti‐Markovnikov hydroamination of alkenes. By using an organocatalytic photoredox system, α‐ and β‐substituted styrenes as well as aliphatic alkenes undergo anti‐Markovnikov hydroamination. Heterocyclic amines were also successfully employed as nitrogen nucleophiles, thus providing a direct route to heterocyclic motifs common in medicinal agents.     

Catalyst-Controlled Regiodivergent and Enantioselective Formal Hydroamination of N,N-Disubstituted Acrylamides to α-Tertiary-α-Aminolactam and β-Aminoamide Derivatives

Enantioenriched α-tertiary-α-aminoacid and α-chiral-β-aminoacid derivatives play an important role in biological science and pharmaceutical chemistry. Thus, the development of methods for their synthesis is highly valuable and yet remains challenging. Herein, an unprecedented catalyst-controlled regiodivergent and enantioselective formal hydroamination of N,N-disubstituted acrylamides with aminating agents has been developed, accessing enantioenriched α-tertiary-α-aminolactam and α-chiral-β-aminoamide derivatives. Sterically-disfavored and electronically-disfavored enantioselective hydroamination of electron-deficient alkenes have been successfully tuned using different transition metals and chiral ligands. Notably, extremely hindered aliphatic α-tertiary-α-aminolactam derivatives were synthesized by Cu−H catalyzed asymmetric C−N bond forming with tertiary alkyl species. Enantioenriched α-chiral-β-aminoamide derivatives have been accessed by Ni−H catalyzed anti-Markovnikov-selective formal hydroaminations of alkenes. This set of reactions tolerates a wide range of functional groups to deliver diverse α-tertiary-α-aminolactam and α-chiral-β-aminoamide derivatives in good yields with high levels of enantioselectivity.     

InBr3 Catalyzed intermolecular hydroamination of unactivated alkenes

InBr₃ has been demonstrated to be a simple catalyst for the intermolecular hydroamination of unactivated alkenes to produce tosyl- and mesyl-protected amines in moderate to good yields.     

Free‐Amine‐Directed Alkenylation of C(sp2)?H and Cycloamination by Palladium Catalysis

A new protocol for the palladium‐catalyzed free‐amine‐directed alkenylation of C(sp²)? H bonds and cycloamination is described. Substituted biaryl‐2‐amines react with various alkenes, including electron‐deficient alkenes, aryl alkenes and alkyl alkenes, to give the corresponding phenanthridines with exclusive regioselectivity. The use of α‐branched styrenes leads to the formation of tricyclic compounds with a seven‐membered amine ring. The method operates through a free‐amine‐directed alkenylation and a subsequent hydroamination cyclization reaction.     

Well‐Defined Four‐Coordinate Iron(II) Complexes For Intramolecular Hydroamination of Primary Aliphatic Alkenylamines

Despite the growing interest in iron catalysis and hydroamination reactions, iron‐catalyzed hydroamination of unprotected primary aliphatic amines and unactivated alkenes has not been reported to date. Herein, a novel well‐defined four‐coordinate β‐diketiminatoiron(II) alkyl complex is shown to be an excellent precatalyst for the highly selective cyclohydroamination of primary aliphatic alkenylamines at mild temperatures (70–90 °C). Both empirical kinetic analyses and the reactivity of an isolated iron(II) amidoalkene dimer, [LFe(NHCH₂CPh₂CH₂CH?CH₂)]₂ favor a stepwise σ‐insertive mechanism that entails migratory insertion of the pendant alkene into an iron–amido bond associated with a rate‐determining aminolysis step.     

Intramolecular hydroamination of aminoalkenes catalyzed by a cationic zirconium complex

A new cationic [N(-)O(-)S]zirconium complex (cat.) was developed to be an excellent catalyst for the intramolecular hydroamination of aminoalkenes with a large substrate scope from terminal alkenes to internal alkenes, and primary amines to secondary amines. The catalyst system can also tolerate various functional groups and perform sequential hydroamination of primary aminodienes.     

Asymmetric hydrogenation of alkenes with planar chiral 2-phosphino-1-aminoferrocene-iridium(I) complexes

The first highly enantioenriched and enantiopure planar chiral 2-phosphino-1-aminoferrocene ligands and their Ir(COD)BAr_F complexes are reported. The ligands display bidentate coordination behavior towards iridium, as indicated by trends in ³¹P and ¹H NMR spectra of the phosphine moieties and the α to nitrogen substituents of the amines. All of the new complexes showed good reactivity as catalysts in promoting asymmetric hydrogenation of several prochiral alkenes, with enantioselectivities up to 92%. Iridium complexes of dimethylaminoferrocene derivatives containing P-Ar groups [PPh₂ and P(o-tol)₂] gave the highest levels of asymmetric induction.     

Zirconium Catalyzed Hydroaminoalkylation for the Synthesis of α-Arylated Amines and N-Heterocycles

The zirconium catalyzed hydroaminoalkylation of alkenes with N-aryl- and sterically demanding N-alkyl-α-arylated secondary amines by using commercially available Zr(NMe₂)₄ is reported. N-phenyl- and N-isopropylbenzylamine are used as amine substrates to establish the alkene substrate scope. Exclusively linear products are obtained in the presence of bulky vinylsilanes. Challenging α-heteroarylated amines and functionalized alkene substrates are compatible with this easy to use catalyst, affording a new disconnection strategy for the atom- and step-economic preparation of selectively substituted saturated α-arylated heterocycles.     

Anti-Markovnikov Hydroamination of Racemic Allylic Alcohols to Access Chiral γ-Amino Alcohols

A ruthenium-catalyzed formal anti-Markovnikov hydroamination of allylic alcohols for the synthesis of chiral γ-amino alcohols is presented. Proceeding via an asymmetric hydrogen-borrowing process, the catalysis allows racemic secondary allylic alcohols to react with various amines, affording enantiomerically enriched chiral γ-amino alcohols with broad substrate scope and excellent enantioselectivities (68 examples, up to >99 % ee).     

Enantioselective hydrogenations of arylalkenes mediated by [Ir(cod) (JM-Phos) ]+ complexes

Phosphine oxazoline ligands la-j were converted to the corresponding [Ir(cod)(phosphine oxazoline)]+ complexes 2a-j. X-ray diffraction analyses of complexes 2b, 2h, 2i, and 2j were performed. The tert-butyl-, 1,1-diphenylethyl-, and phenyl-oxazoline complexes (2b, 2h, and 2i, respectively) had typical square planar metal environments with chair-like metallocyclic rings. However, the 3,5-di-tert-butylphenyl oxazoline complex 2j was distorted toward a tetrahedral metal geometry. This library of complexes was tested in asymmetric hydrogenations of several arylalkenes. High enantioselectivities and conversions were observed for some substrates. A possible special role for the HPh2C-oxazoline substituent in asymmetric hydrogenations was identified and is discussed. In attempts to rationalize why high enantioselectivities were not observed for some alkenes, a series of deuterium labeling experiments were performed to probe for competing reactions that occurred prior to the hydrogenation step. Double bond migrations were inferred for several substrates, and this is a significant complication in asymmetric hydrogenations of arylalkenes that had not been discussed prior to this study. A mechanistic rationale is proposed involving competing double bond migration for some but not all substrates. Appreciation of this complication will be valuable in further studies aimed at optimization of enantioselection in asymmetric hydrogenations of unfunctionalized alkenes.     

Chiral Brønsted Acid Catalyzed Dynamic Kinetic Asymmetric Hydroamination of Racemic Allenes and Asymmetric Hydroamination of Dienes

The first highly efficient and practical chiral Brønsted acid catalyzed dynamic kinetic asymmetric hydroamination (DyKAH) of racemic allenes and asymmetric hydroamination of unactivated dienes with both high E/Z selectivity and enantioselectivity are described herein. The transformation proceeds through a new catalytic asymmetric model involving a highly reactive π‐allylic carbocationic intermediate, generated from racemic allenes or dienes through a proton transfer mediated by an activating/directing thiourea group. This method affords expedient access to structurally diverse enantioenriched, potentially bioactive alkenyl‐containing aza‐heterocycles and bicyclic aza‐heterocycles.     

Hydroamination of Carbonyl Compounds with Oximes

N-alkyl(cycloalkyl)benzylamines, p-fluorobenzylamines, (1-phenylethyl)amines, [1-(p-fluorophenyl)ethyl]amines were synthesized by hydroamination of aldehydes and ketones with oximes.     

Cobalt‐Catalyzed Enantioselective Synthesis of Chiral gem‐Bis(boryl)alkanes

We report an asymmetric synthesis of enantioenriched gem‐bis(boryl)alkanes in an enantioselective diborylation of 1,1‐disubstituted alkenes catalyzed by Co(acac)₂/(R)‐DM‐segphos. A range of activated and unactivated alkenes underwent this asymmetric diborylation in the presence of cyclooctene as a hydrogen acceptor, affording the corresponding gem‐bis(boryl)alkanes with high enantioselectivity. The synthetic utility of these chiral organoboronate compounds was demonstrated through several stereospecific derivatizations and the synthesis of sesquiterpene and sesquiterpenoid natural products.     

Highly Enantioselective Iron‐Catalyzed cis‐Dihydroxylation of Alkenes with Hydrogen Peroxide Oxidant via an FeIII‐OOH Reactive Intermediate

The development of environmentally benign catalysts for highly enantioselective asymmetric cis‐dihydroxylation (AD) of alkenes with broad substrate scope remains a challenge. By employing [Fe^II(L)(OTf)₂] (L=N,N′‐dimethyl‐N,N′‐bis(2‐methyl‐8‐quinolyl)‐cyclohexane‐1,2‐diamine) as a catalyst, cis‐diols in up to 99.8 % ee with 85 % isolated yield have been achieved in AD of alkenes with H₂O₂ as an oxidant and alkenes in a limiting amount. This “[Fe^II(L)(OTf)₂]+H₂O₂” method is applicable to both (E)‐alkenes and terminal alkenes (24 examples >80 % ee, up to 1 g scale). Mechanistic studies, including ¹⁸O‐labeling, UV/Vis, EPR, ESI‐MS analyses, and DFT calculations lend evidence for the involvement of chiral Fe^III‐OOH active species in enantioselective formation of the two C?O bonds.     

Asymmetric Hydrocyanation of Alkenes without HCN

A general and efficient rhodium‐catalyzed asymmetric cyanide‐free hydrocyanation of alkenes has been developed. Based on the asymmetric hydroformylation/condensation/aza‐Cope elimination sequences, a broad scope of substrates including mono‐substituted, 1,2‐, and 1,1‐disubstituted alkenes (involving natural product R‐ and S‐limonene) were employed, and a series of valuable chiral nitriles are prepared with high yields (up to 95 %) and enantioselectivities (up to 98 % ee). Notably, the critical factor to achieve high enantioseletivies is the addition of catalytic amount of benzoic acid. This novel methodology provides an efficient and concise synthetic route to the intermediate of vildagliptin and anagliptin.     

Early Main Group Metal Catalysis: How Important is the Metal?

Organocalcium compounds have been reported as efficient catalysts for various alkene transformations. In contrast to transition metal catalysis, the alkenes are not activated by metal–alkene orbital interactions. Instead it is proposed that alkene activation proceeds through an electrostatic interaction with a Lewis acidic Ca²⁺. The role of the metal was evaluated by a study using the metal‐free catalysts: [Ph₂N^?][Me₄N⁺] and [Ph₃C^?][Me₄N⁺]. These “naked” amides and carbanions can act as catalysts in the conversion of activated double bonds (C?O and C?N) in the hydroamination of Ar? N?C?O and R? N?C?N? R (R=alkyl) by Ph₂NH. For the intramolecular hydroamination of unactivated C?C bonds in H₂C?CHCH₂CPh₂CH₂NH₂ the presence of a metal cation is crucial. A new type of hybrid catalyst consisting of a strong organic Schwesinger base and a simple metal salt can act as catalyst for the intramolecular alkene hydroamination. The influence of the cation in catalysis is further evaluated by a DFT study.     

Early Main Group Metal Catalysis: How Important is the Metal?

Organocalcium compounds have been reported as efficient catalysts for various alkene transformations. In contrast to transition metal catalysis, the alkenes are not activated by metal–alkene orbital interactions. Instead it is proposed that alkene activation proceeds through an electrostatic interaction with a Lewis acidic Ca²⁺. The role of the metal was evaluated by a study using the metal‐free catalysts: [Ph₂N⁻][Me₄N⁺] and [Ph₃C⁻][Me₄N⁺]. These “naked” amides and carbanions can act as catalysts in the conversion of activated double bonds (CO and CN) in the hydroamination of Ar NCO and R NCN R (R=alkyl) by Ph₂NH. For the intramolecular hydroamination of unactivated CC bonds in H₂CCHCH₂CPh₂CH₂NH₂ the presence of a metal cation is crucial. A new type of hybrid catalyst consisting of a strong organic Schwesinger base and a simple metal salt can act as catalyst for the intramolecular alkene hydroamination. The influence of the cation in catalysis is further evaluated by a DFT study.     

Effect of solvent on the free energy of activation of S_N2 reaction between phenacyl bromide and amines

The kinetics of SN2 reaction between phenacyl bromide and various amines in 12 different solvents were studied. Solvent effects on the rate of this reaction and free energy of activation, ΔG# , were interpreted by applying the Abraham-Kam-let-Taft (AKT) equation. UK solvent polarity (π1*), solvent hydrogen-bond basicity (β1) and Hildebrand cohesive density energy (δH2) are those parameters which increase the rate constant and decrease ΔG# , while solvent hydrogen-bond acidity (α1) will have the compensatory effect. A comparison among obtained values of second rate constants, k2, for different amines in a given solvent indicates that the amine reactivities are highly dependent on their structures. The consequent decrease of the rate constant for different amines in any given solvent was found to be: primary > secondary> tertiary. This order results from steric effects of amines.     

Asymmetric Conjugate Addition of Unmodified Cyclic Ketones to Nitroolefins Using Aminophosphonate as the Organocatalyst

本文设计合成了光学纯吡咯烷基磷酸酯,并成功地应用于酮类底物与b-硝基芳基乙烯衍生物的不对称催化Michael加成反应中。在20 mol %催化剂用量下,以10 mol %三氟乙酸作为添加物,无溶剂条件下,0 oC反应7-24小时,Michael加成产物的收率最高达96%,非对映选择性最高可达97:3,ee值最高可达90%。     

An approach to α-substituted amines

A number of amines have been alkylated at the position alpha to nitrogen via free radical methodology. N-(2-Iodobenzyl) and N-(2-iodobenzoyl)‘protected’ amines have been used to generate radicals which rapidly undergo a 1,5-hydrogen shift to give more stable α-amino radicals. These can subsequently be trapped by electron deficient alkenes to give α-alkylated amines.