Mechanistic Studies and Expansion of the Substrate Scope of Direct Enantioselective Alkynylation of α-Ketiminoesters Catalyzed by Adaptable (Phebox)Rhodium(III) Complexes

Redox-Active α-Amino-CF3 Reagents: Developing and Applications in Ni-Catalyzed Reductive Cross-Coupling

α-Amino-CF3 compounds are widely employed in bio- and pharmaceutical chemistry for improved stability and bioactivities. Traditional methods often face challenges with functional group tolerance and lack a general approach for late-stage functionalization. Herein, we report a new type of redox-active α-amino-CF3 reagents, easily prepared from trifluoro acetaldehyde hydrates. These α-amino-CF3 reagents can serve as versatile building blocks for coupling with alkynyl bromides, aryl bromides, and enol triflates under nickel catalysis.

Dual Nickel- and Photoredox-Catalyzed Asymmetric Reductive Cross-Couplings: Just a Change of the Reduction System?

ConspectusIn recent years, nickel-catalyzed asymmetric coupling reactions have emerged as efficient methods for constructing chiral C(sp3) carbon centers. Numerous novel approaches have been reported to rapidly construct chiral carbon-carbon bonds through nickel-catalyzed asymmetric couplings between electrophiles and nucleophiles or asymmetric reductive cross-couplings of two different electrophiles. Building upon these advances, our group has been devoted to interrogating dual nickel- and photoredox-catalyzed asymmetric reductive cross-coupling reactions.In our endeavors over the past few years, we have successfully developed several dual Ni-/photoredox-catalyzed asymmetric reductive cross-coupling reactions involving organohalides. While some probably think that this system is just a change of the reduction system from traditional metal reductants to a photocatalysis system, a question that we also pondered at the beginning of our studies, both the achievable reaction types and mechanisms suggest a different conclusion: that this dual catalysis system has its own advantages in the chiral carbon-carbon bond formation. Even in certain asymmetric reactions where the photocatalysis regime functions only as a reducing system, the robust reducing capability of photocatalysts can effectively accelerate the regeneration of low-valent nickel species, thus expanding the selectable scope of chiral ligands. More importantly, in many transformations, besides reducing nickel catalysts, the photocatalysis system can also undertake the responsibility of alkyl radical formation, thereby establishing two coordinated, yet independent catalytic cycles. This catalytic mode has been proven to play a crucial role in achieving diverse asymmetric coupling reactions with great challenges.In this Account, we elucidate our understanding of this system based on our experience and findings. In the Introduction, we provide an overview of the main distinctions between this system and traditional Ni-catalyzed asymmetric reductive cross-couplings with metal reductants and the potential opportunities arising from these differences. Subsequently, we outline various chiral carbon-carbon bond-forming types obtained by this dual Ni/photoredox catalysis system and their mechanisms. In terms of chiral C(sp3)-C(sp2) bond formation, extensive discussion focuses on the asymmetric arylations of α-chloroboronates, α-trifluoromethyl alkyl bromides, α-bromophosphonates, and so on. In the realm of chiral C(sp3)-C(sp) bond formation, asymmetric alkynylations of α-bromophosphonates and α-trifluoromethyl alkyl bromides have been presented herein. Regarding C(sp3)-C(sp3) bond formation, we take the asymmetric alkylation of α-chloroboronates as a compelling example to illustrate the great efficiency of this dual catalysis system. This summary would enable a better grasp of the advantages of this dual catalysis system and clarify how the photocatalysis regime facilitates enantioselective transformations. We anticipate that this Account will offer valuable insights and contribute to the development of new methodologies in this field.

Enantioselective propargylic amination and related tandem sequences to α-tertiary ethynylamines and azacycles

Chiral α-tertiary amines and related azacycles are sought-after compounds for drug development. Despite progress in the catalytic asymmetric construction of aza-quaternary stereocentres, enantioselective synthesis of multifunctional α-tertiary amines remains underdeveloped. Enantioenriched α-disubstituted α-ethynylamines are attractive synthons for constructing chiral α-tertiary amines and azacycles, but methods for their catalytic enantioselective synthesis need to be expanded. Here we describe an enantioselective asymmetric Cu(I)-catalysed propargylic amination (ACPA) of simple ketone-derived propargylic carbonates to give both α-dialkylated and α-alkyl-α-aryl α-tertiary ethynylamines. Sterically confined pyridinebisoxazoline (PYBOX) ligands, with a C4 shielding group and relaying groups, play a key role in achieving excellent enantioselectivity. The syntheses of quaternary 2,5-dihydropyrroles, dihydroquinines, dihydrobenzoquinolines and dihydroquinolino[1,2-α]quinolines are reported, and the synthetic value is further demonstrated by the enantioselective catalytic total synthesis of a selective multi-target β-secretase inhibitor. Enantioselective Cu-catalysed propargylic substitutions with O- and C-centred nucleophiles are also realized, further demonstrating the potential of the PYBOX ligand.

Challenges and recent advancements in the synthesis of α,α-disubstituted α-amino acids

α,α-Disubstituted α-amino acids (α-AAs) have improved properties compared to other types of amino acids. They serve as modifiers of peptide conformation and as precursors of bioactive compounds. Therefore, it has been a long-standing goal to construct this highly valuable scaffold efficiently in organic synthesis and drug discovery. However, access to α,α-disubstituted α-AAs is highly challenging and largely unexplored due to their steric constraints. To overcome these, remarkable advances have been made in the last decades. Emerging strategies such as synergistic enantioselective catalysis, visible-light-mediated photocatalysis, metal-free methodologies and CO2 fixation offer new avenues to access the challenging synthesis of α,α-disubstituted α-AAs and continuously bring additional contributions to this field. This review article aims to provide an overview of the recent advancements since 2015 and discuss existing challenges for the synthesis of α,α-disubstituted α-AAs and their derivatives.

Enantioselective Alkynylation of 2-Aryl-3H-indol-3-ones via Cooperative Catalysis of Copper/Chiral Phosphoric Acid

A facile enantioselective alkynylation of cyclic ketimines attached to a neutral functional group utilizing the dual Cu(I)-CPA catalysis is described. The strategy of the alkynylation of 2-aryl-3H-indol-3-one directly to chiral propargylic amines containing indolin-3-one moiety in good yields and enantioselectivities. Moreover, gram-scale synthesis of chiral propargylamines based C2-quaternary indolin-3-ones was performed. The synthetic applications were confirmed by transformations of the products with no decrease in the yield and enantioselectivity.

Microwave-assisted rapid synthesis of chiral oxazolines

Chiral oxazoline compounds play an extremely important role in asymmetric synthesis and drug discovery. Herein a simpler, greener and more efficient microwave-assisted protocol to rapidly access chiral oxazolines is developed using aryl nitriles or cyano-containing compounds and chiral β-amino alcohols as starting materials. The reaction proceeds smoothly in the presence of a recoverable heterogeneous catalyst in either concentrated solution or under solvent-free conditions. The advantages of this method include rapidness, convenience, environmental protection, high atom economy, and excellent yields. The protocol should find wider application in the community in the future.

Coordination Assistance: A Powerful Strategy for Metal-Catalyzed Regio- and Enantioselective Hydroalkynylation of Internal Alkenes

ConspectusAlkenes are versatile compounds that are readily available on a large scale from industry or through organic synthesis. The widespread occurrence of alkenes provides the continuous impetus for the development of catalytic asymmetric alkene hydrofunctionalizations, which enables expeditious construction of complex chiral molecules from readily available starting materials. Catalytic asymmetric hydrofunctionalization of internal alkenes presents a notable challenge, due to their low reactivity, many potential side reactions, and the simultaneous control of the regio-, diastereo-, and enantioselectivities.Dehydroamino acids and enamides are among the first substrates that provide notable enantioselectivities in catalytic asymmetric hydrogenation. The crucial importance of an amide coordinating group is established by a series of classical mechanistic studies. This initial success greatly stimulated further development for catalytic hydrogenation and hydrofunctionalization. Building on these pioneering works in asymmetric hydrogenation as well as related hydrofunctionalizations, we have adopted coordination assistance as a powerful tool to address the challenges associated with the asymmetric hydrofunctionalization of internal alkenes. Using a functional group on the alkene substrate as a native coordinating group, a two-point binding mode of the substrate to the metal center effectively enhances the reactivity and facilitates the control of regio-, diastereo- and enantioselectivities. Through this strategy, we have developed a number of alkene hydrofunctionalization methods with excellent regio-, diastereo-, and enantiocontrols.In this Account, we summarize the recent advance in our lab using coordination assistance as a key element to achieve regio- and enantioselective hydroalkynylation of internal alkenes. First, we describe our early work aimed at controlling the regio- and enantioselectivity of hydroalkynylation using disubstituted enamide as the substrate. Both α- and β-alkynylation were achieved by channeling the reaction pathway into a Chalk-Harrod or modified Chalk-Harrod mechanism. Next, we discuss the further development of catalysts to achieve regiodivergent and enantioselective hydroalkynylation of trisubstituted enamide to access vicinal stereocenters and quaternary carbon stereocenters. We also discuss the hydroalkynylation of α,β-unsaturated amides to achieve unconventional site-selectivity through a combination of alkene isomerization and regioselective hydroalkynylation. This provides the basis for the construction of a remote quaternary carbon stereocenter through catalytic hydroalkynylation of trisubstituted β,γ-unsaturated amides. We further show that this controlling principle is applicable to terminal alkene with a coordinating group as well. A ligand-controlled mechanism shift is discussed for the enantioselective alkynylation at the terminal and internal position of 1,1,-disubstituted alkenes. Finally, we briefly mention the application of coordination assistance to other hydrofunctionalizations such as hydroboration and hydrosilylation, where previously inaccessible reactivity and selectivity were achieved. Collectively, these catalytic methods demonstrate the power of coordination assistance for enantioselective hydrofunctionalizations. We anticipate that this strategy will create a platform to enable diverse enantioselective alkene transformations.

Recent advances in the synthesis of fluorinated amino acids and peptides

The site-selective modification of amino acids, peptides, and proteins has always been an intensive topic in organic synthesis, medicinal chemistry, and chemical biology due to the vital role of amino acids in life. Among the developed methods, the site-selective introduction of fluorine functionalities into amino acids and peptides has emerged as a useful approach to change their physicochemical and biological properties. With the increasing demand for life science, the direct fluorination/fluoroalkylation of proteins has also received increasing attention because of the unique properties of fluorine atom(s) that can change the protein structure, increase their lipophilicity, and enable fluorine functionality as a biological tracer or probe for chemical biology studies. In this feature article, we summarized the recent advances in the synthesis of fluorinated amino acids and peptides, wherein two strategies have been discussed. One is based on the fluorinated building blocks to prepare fluorinated amino acids and peptides with diversified structures, including the transformations of fluorinated imines and nickel-catalyzed dicarbofunctionalization of alkenes with bromodifluoroacetate and its derivatives; the other is direct fluorination/fluoroakylation of amino acids, peptides, and proteins, in which the selective transformations of the functional groups on serine, threonine, tyrosine, tryptophan, and cysteine lead to a wide range of fluorinated α-amino acids, peptides, and proteins, featuring synthetic convenience and late-stage modification of biomacromolecules. These two strategies complement each other, wherein transition-metal catalysis and new fluoroalkylating reagents provide powerful tools to selectively access fluorinated amino acids, peptides, and proteins, showing the prospect of medicinal chemistry and chemical biology.

[Development of Unactivated Bond Cleavage Reactions Under Mild Conditions Based on Stabilization of Addition Intermediates]

Cleavage of unactivated bonds, such as amides, often requires challenging reaction conditions with strong acids and bases, and the tolerance of functional groups is limited. Therefore, the development of cleavage reactions for unactivated bonds under mild reaction conditions is essential. Herein, I report our recent developments in the cleavage of unactivated bonds under mild conditions. We achieved cleavage of unactivated amides, carbamates, ureas, and esters, as well as chemoselective cleavage of directing groups. Furthermore, we conducted mechanistic studies and found that these reactions proceed through the stabilization of addition intermediates.

Direct Enantioselective Addition of Alkynes to Imines by a Highly Efficient Palladacycle Catalyst

Enantiopure propargylic amines are highly valuable synthetic building blocks. Much effort has been devoted to develop methods for their preparation. The arguably most important strategy is the 1,2-addition of alkynes to imines. Despite remarkable progress, the known methods using Zn and Cu catalysts suffer from the need for high catalyst loadings, typically ranging from 2-60 mol % for neutral aldimine substrates. Here we report a planar chiral Pd complex acting as very efficient catalyst for direct asymmetric alkyne additions to imines, requiring very low catalyst loadings. Turnover numbers of up to 8700 were accomplished. Our investigation suggests that a Pd-acetylide complex is generated as a catalytically relevant intermediate by the aid of an acac ligand acting as internal catalytic base. It is shown that the catalyst is quite stable under the reaction conditions and that product inhibition is not an issue. A total of 39 examples is shown which all yielded almost enantiopure products.

Mechanistic Study of Asymmetric Alkynylation of Isatin-Derived Ketimine Mediated by a Copper/Guanidine Catalyst

In this work, we performed a mechanistic study of asymmetric alkynylation of isatin-derived N-Boc ketimine that was first reported by Feng, Liu, and co-workers (Chem. Commun. 2018, 54, 678-681). Guanidine-amide promoted the formation of highly nucleophilic copper acetylene species by abstracting the terminal proton of phenylacetylene with an imine moiety. The guanidinium salt-Cu(I) complex was the most active species in the addition of the C═N bond, in which copper acetylene coordinated to the O atom of the amide moiety, and the isatin-derived ketimine substrate was activated by hydrogen bonding as well as tert-butoxycarbonyl···Cu(I) coordination. Due to weak interaction between Cu(I) and the Ph group in the amide of guanidine, as well as the repulsion between the tert-butyl group in ketimine and the cyclohexyl group in guanidine, the copper acetylene preferred to attack isatin-derived ketimine from the re-face, leading to the S-configuration product with excellent stereoselectivity. The affinity of the counterion for the Cu(I) center in the copper salt affected the deprotonation of phenylacetylene and the formation of guanidinium salt active species. In contrast to CuBr and CuCl, the combination of CuI with aniline-derived guanidine-amide exhibited high catalytic activity and a chiral induction effect, contributing to a high turnover frequency (9.70 × 10^-4 s^-1) in catalysis and ee%.

Amide phosphonium salt catalyzed enantioselective Mannich addition of isoxazole-based nucleophiles to β,γ-alkynyl-α-ketimino esters

An enantioselective Mannich addition of 3,5-disubstituted 4-nitroisoxazoles to β,γ-alkynyl-α-ketimino esters promoted by an amide phosphonium salt-based catalyst has been developed. N-Cbz-protected ketimino esters with various aryl substituents attached to the alkyne unit were reacted with a series of isoxazoles with different substitution patterns. Chiral tertiary propargylic amine products were obtained with moderate to good yields and enantioselectivities. TIPS- and cyclopropyl-substituted alkynyl ketimines were also examined in the current system and the desired products were obtained with moderate yields and enantioselectivities. The potential scalability and utility of the current protocol were demonstrated by carrying out a relatively larger scale reaction followed by further transformations.

Water enables diastereodivergency in bispidine-based chiral amine-catalyzed asymmetric Mannich reaction of cyclic N-sulfonyl ketimines with ketones

Tuning diastereoselectivity is a great challenge in asymmetric catalysis for the inherent stereochemical bias of the substrates. Here, we report a diastereodivergent asymmetric Mannich reaction of cyclic N-sulfonyl ketimines with ketones catalyzed by a bispidine-based chiral amine catalyst, in which additional water switches the diastereoselectivity efficiently. Both chiral anti- and syn-benzosultams with potential anti-HIV-1 activity are obtained in excellent yields and good to excellent ee values. Control experiments and density functional theory (DFT) calculations were applied to study the diastereodivergent mechanism, which reveal that the diastereodivergent catalysis should be state-determined, and the water reverses the energies of states to realize the diastereodivergency. The findings are quite new and might inspire more diastereodivergent asymmetric synthesis.

A diastereodivergent asymmetric Mannich reaction of cyclic N-sulfonyl ketimines with ketones is realized by employing bispidine-based chiral amine as catalyst and additional water switching the diastereoselectivity.

Practical asymmetric amine nucleophilic approach for the modular construction of protected α-quaternary amino acids

We report the first amine nucleophilic approach for the modular construction of enantioenriched protected α-quaternary amino acids. The key to success is the use of an alcohol solvent, which makes a rationally designed COOMe-bonded Cu-allenylidene electrophilic intermediate stable enough to couple with amine nucleophiles before its decomposition. The reaction features wide functional group tolerance with high enantioselectivity, typically >90% ee, and is amenable to the modification of commercially available bioactive molecules. The resultant protected α-amino acids could be readily converted into a number of precious enantioenriched amines featuring α-hindered tertiary carbon centers, which are otherwise synthetically quite challenging, including those of α-amino aldehyde, peptides or α-vinyl amino ester with >92% ee in excellent yields. This protocol could be utilized for the synthesis of the protected bioactive α-ethylnorvaline in 3 steps, a significant advancement in comparison to an 11-step sequence reported previously.

We report the first amine nucleophilic approach for the modular construction of enantioenriched protected α-quaternary amino acids.

Organocatalytic asymmetric synthesis of quaternary α-isoxazole–α-alkynyl amino acid derivatives

Chiral phosphoric acid catalyzed enantioselective addition of 5-amino-isoxazoles with β,γ-alkynyl-α-ketimino esters provided good yields and excellent enantioselectivities.

Unmasking the reverse reactivity of cyclic N-sulfonyl ketimines: multifaceted applications in organic synthesis

The chemistry related to the exploration of cyclic N-sulfonyl ketimines and their derivatives has attracted significant attention in the last few decades because of their intriguing structures and properties. They serve broadly as reactive synthons in various reactions to create a diverse set of synthetically and biologically attractive molecules. Furthermore, these moieties, which possess multiple heteroatoms (N, O and S), display or can enhance many biological activities. In the case of synthetic reactions, chemists mainly focus on the chemical manipulation of the highly reactive prochiral CN bond of N-sulfonyl ketimines. Besides their traditional role as electrophiles, N-sulfonyl ketimines possess α-Csp³-H protons, and thus behave as potential carbonucleophiles, where they can undergo several C-X (X = C, N and O) bond-forming reactions with different types of electrophiles under various conditions to form a wide range of fascinating asymmetric and non-asymmetric versions of fused heterocycles, carbocycles, spiro-fused skeletons, pyridines, pyrroles, etc. Herein, we highlight the recent examples from our research work and others covering the scope of cyclic N-sulfonyl ketimines as useful carbonucleophiles. In addition, the detailed mechanistic studies of the above-mentioned reactions are also presented.

Cu(I)-Catalyzed gem-Aminoalkynylation of Diazo Compounds: Synthesis of Fluorinated Propargylic Amines

The gem-aminoalkynylation of fluorinated diazo compounds catalyzed by a simple Cu(I) salt is described. This three-component reaction allows the synthesis of propargylic amines with broad functional group tolerance. Both electron-rich and electron-poor anilines can be used as nucleophiles and alkyl-, aryl-, and silyl-substituted EthynylBenziodoXoles (EBX) as electrophiles.

Further Developments and Applications of Oxazoline-Containing Ligands in Asymmetric Catalysis

The chiral oxazoline motif is present in many ligands that have been extensively applied in a series of important metal-catalyzed enantioselective reactions. This Review aims to provide a comprehensive overview of the most significant applications of oxazoline-containing ligands reported in the literature starting from 2009 until the end of 2018. The ligands are classified not by the reaction to which their metal complexes have been applied but by the nature of the denticity, chirality, and donor atoms involved. As a result, the continued development of ligand architectural design from mono(oxazolines), to bis(oxazolines), to tris(oxazolines) and tetra(oxazolines) and variations thereof can be more easily monitored by the reader. In addition, the key transition states of selected asymmetric transformations will be given to illustrate the features that give rise to high levels of asymmetric induction. As a further aid to the reader, we summarize the majority of schemes with representative examples that highlight the variation in % yields and % ees for carefully selected substrates. This Review should be of particular interest to the experts in the field but also serve as a useful starting point to new researchers in this area. It is hoped that this Review will stimulate both the development/design of new ligands and their applications in novel metal-catalyzed asymmetric transformations.

Asymmetric Synthesis of Tetrasubstituted α-Aminophosphonic Acid Derivatives

Due to their structural similarity with natural α-amino acids, α-aminophosphonic acid derivatives are known biologically active molecules. In view of the relevance of tetrasubstituted carbons in nature and medicine and the strong dependence of the biological activity of chiral molecules into their absolute configuration, the synthesis of α-aminophosphonates bearing tetrasubstituted carbons in an asymmetric fashion has grown in interest in the past few decades. In the following lines, the existing literatures for the synthesis of optically active tetrasubstituted α-aminophosphonates are summarized, comprising diastereoselective and enantioselective approaches.

Strategies for the Catalytic Enantioselective Synthesis of α-Trifluoromethyl Amines

The exploitation of the α-trifluoromethylamino group as an amide surrogate in peptidomimetics and drug candidates has been on the rise. In a large number of these cases, this moiety bears stereochemistry with the stereochemical identity having important consequences on numerous molecular properties, such as the potency of the compound. Yet, the majority of stereoselective syntheses of α-CF3 amines rely on diastereoselective couplings with chiral reagents. Concurrent with the rapid expansion of fluorine into pharmaceuticals has been the development of catalytic enantioselective means of preparing α-trifluoromethyl amines. In this work, we outline the strategies that have been employed for accessing these enantioenriched amines, including normal polarity approaches and several recent developments in imine umpolung transformations.

Catalytic asymmetric synthesis of quaternary trifluoromethyl α- to ε-amino acid derivatives via umpolung allylation/2-aza-Cope rearrangement

In this study, we developed an efficient Ir-catalyzed cascade umpolung allylation/2-aza-Cope rearrangement of tertiary α-trifluoromethyl α-amino acid derivatives for the preparation of a variety of quaternary α-trifluoromethyl α-amino acids in high yields with excellent enantioselectivities. The umpolung reactivity empowered by the activation of the key isatin-ketoimine moiety obviates the intractable enantioselectivity control in Pd-catalyzed asymmetric linear α-allylation. In combination with quasi parallel kinetic resolution or kinetic resolution, the generality of this method is further demonstrated by the first preparation of enantioenriched quaternary trifluoromethyl β-, γ-, δ- and ε-amino acid derivatives.

A Broad Substrate Scope of Aza-Friedel-Crafts Alkylation for the Synthesis of Quaternary α-Amino Esters

A versatile synthetic protocol of aza-Friedel-Crafts alkylation has been developed for the synthesis of quaternary α-amino esters. This operationally simple alkylation proceeds under ambient conditions with high efficiency, regioselectivity, and an exceptionally broad scope of arene nucleophiles. A key feature of this alkylation is the role associated with the silver(I) salt counteranions liberated during the reaction. Taking advantage of a phase-transfer counteranion/Brønsted acid pair mechanism, we also report a catalytic enantioselective example of the reaction.

Copper-Catalyzed Enantioselective Synthesis of Oxazolines from Aminotriols via Asymmetric Desymmetrization

A copper-catalyzed enantioselective transformation of tris(hydroxymethyl)aminomethane-derived aminotriols was developed to provide multisubstituted oxazolines with a tetrasubstituted carbon center. The present transformation consisted of sequential reactions involving mono-sulfonylation of aminotriols, subsequent intramolecular cyclization to afford prochiral oxazoline diols, and sulfonylative asymmetric desymmetrization of resultant oxazoline diols. In addition, the kinetic resolution process would be involved in the sulfonylative asymmetric desymmetrization step, which would amplify the enantiopurities of the desired products. Various aminotriols were tolerated in the present reaction, affording the desired oxazolines in good to high yields with excellent enantioselectivities. The synthetic utility of the present reaction was demonstrated by the transformation of the optically active oxazoline into a chiral α-tertiary amine motif.

Asymmetric synthesis of quaternary α-trifluoromethyl α-amino acids by Ir-catalyzed allylation followed by kinetic resolution

Facile access to quaternary α-trifluoromethyl α-amino acids has been developed. This sequential reaction involves an Ir-catalyzed asymmetric allylation of α-trifluoromethyl aldimine esters followed by an unprecedented kinetic resolution.

Pd-Catalyzed Allylation of Imines to Access α-CF3-Substituted α-Amino Acid Derivatives

We herein report a high yielding protocol for the direct α-allylation of easily accessible trifluoropyruvate-derived imines using Pd-catalysis. The reaction gives access to a variety of different α-allylated-α-CF3-amino acids in a straightforward manner, starting from commercially available trifluoropyruvate. We also provide a proof-of-concept for an enantioselective protocol (up to er = 75:25) by using chiral phosphane ligands.

Double Addition of Alkynyllithium Reagents to Amides/Lactams: A Direct and Flexible Synthesis of 3-Amino-1,4-diynes Bearing an Aza-Quaternary Carbon Center

An efficient and mild protocol for the direct and flexible synthesis of 3-amino-1,4-diynes bearing an aza-quaternary carbon from tertiary amides and lactams has been established. The one-pot method consists of in situ activation of amides with trifluoromethanesulfonic anhydride, followed by double addition of alkynyllithium reagents at a concentration of 0.5 mol·L^-1 in dichloromethane. This constitutes an extension of the method of direct reductive bisalkylation of amides that allows both employing alkynyllithium reagents as the first-addition nucleophiles and incorporating an alkynyl group as the first-introduced group.

Synthesis of α-CF3-proline derivatives by means of a formal (3 + 2)-cyclisation between trifluoropyruvate imines and Michael acceptors

We herein report the first formal (3 + 2)-cyclisation between 3,3,3-trifluoropyruvate-derived imines and indandione-based Michael acceptors. This reaction gives access to a novel class of spirocyclic α-CF3-α-proline derivatives with complete control of the diastereoselectivity under phase transfer-catalysed reaction conditions.

Modulation of the coordination geometries of NCN and NCNC Rh complexes for ambidextrous chiral catalysts

A chirality switch between novel NCN pincer Rh complexes and a related double cyclometalated NCNC Rh complex containing secondary amino groups is described.