Enantioconvergent transformations of secondary alcohols through borrowing hydrogen catalysis

Stereodivergent Ruthenium/Copper Relay Catalysis for Modular Access to δ-Lactones with Two Nonadjacent Carbon Stereocenters

The stereodivergent synthesis of δ-lactones, which are prevalent in natural product frameworks, from simple starting materials via a single transformation remains a significant challenge. Herein, we report an enantio- and diastereodivergent cascade reaction for the modular synthesis of chiral δ-lactones bearing two nonadjacent quaternary and tertiary carbon stereocenters. This approach employs bimetallic Ru/Cu relay catalysis between allylic alcohols and azaaryl acetates. This method integrates Ru-catalyzed asymmetric borrowing hydrogen reaction, Cu-catalyzed asymmetric Michael addition, and rapid lactonization into a one-pot process, with all catalysts and substrates introduced at the outset. By orthogonal permutation of two chiral metal catalysts, precise control over the relative and absolute configurations of the newly formed nonadjacent stereocenters is achieved, allowing selective access to all stereoisomers of the δ-lactone products in a predictable and efficient manner.

Asymmetric Vicinal and Remote Hydroamination of Olefins by Employing a Heck-Reaction-Derived Hydride Source

Metal hydrides are reactive intermediates in numerous catalytic processes. In many catalytic processes, metal hydrides are formed, but their potential reactivity is often wasted by reaction with a base or an oxidant to permit catalyst turnover. In this report, the hydroamination of unactivated olefins is described by coupling a Heck reaction with a hydroamination reaction between aryl boronic acid, olefin, and a nitrene precursor dioxazolone. Initiated by a Heck reaction between the olefin and arylboroic acid, a rhodium hydride intermediate is generated and is retained for the hydroamination of a second equivalent of the olefin. Depending on the chain length of the alkyl group of the olefin, α- or β-amino amides were obtained in excellent regio- and enantioselectivity via direct or remote (migratory) hydroamination, respectively. The coupling system features a broad scope, mild conditions, and excellent enantioselectivity, and it also represents a rare example of asymmetric olefin hydroamination using a chiral rhodium(III) cyclopentadienyl catalyst. Mechanistic studies delineated the turnover-limiting and enantio-determining steps of this catalytic system.

Ternary Aldehyde-Copper-Iridium Catalysis Enables Stereodivergent Allylation via α-C-H Functionalization of Primary Amines

α-Chiral primary amines are recognized as one of the most valuable and versatile synthetic intermediates, widely utilized in the construction of diverse amine-containing natural products, pharmaceuticals, and agrochemicals. The direct asymmetric α-C-H functionalization of unprotected primary amines is the most straightforward method for creating these motifs. However, this transformation remains underdeveloped, particularly in stereodivergent synthesis of primary amines with multiple stereocenters. Herein, we report an aldehyde/copper/iridium ternary catalytic system, which was successfully employed for the direct enantio- and diastereodivergent α-allylation of primary α-amino-chromanone without requiring additional protection or activation of the NH2 group. A wide range of α-tertiary primary amines bearing vicinal stereocenters were prepared in high yields with excellent enantio- and diastereoselectivities (generally >20:1 dr and >99% ee). Notably, all four stereoisomers of the α-tertiary amines can be readily prepared by simply switching the configuration combinations of the two chiral metal catalysts. Furthermore, the asymmetric induction model for the α-C-H functionalization of primary amines was meticulously elucidated through comprehensive density functional theory (DFT) calculations.

Molybdenum-Catalyzed Asymmetric Amination of α-Hydroxy Esters: Synthesis of α-Amino Acids

Unnatural α-amino acids are found in a wide variety of bioactive compounds ranging from proteins to pharmaceutical agents to materials science. As a result, the investigation of efficient and simple methods for their synthesis is a major purpose in reaction development. In this study, it is found that a catalyst based on molybdenum, an earth-abundant transition metal, can facilitate the amination of readily accessible α-hydroxy esters to afford N-protected unnatural α-amino acid esters in high yield. This simple process also enables enantioselective amination, which proceeds through cooperative catalysis of chiral molybdenum complex with chiral phosphoric acid (CPA), and complements earlier procedures to the catalytic synthesis of this important class of compounds. The obtained protected α-amino acid ester products are directly useful or further utilized for the synthesis of commercially available drugs and analogs.

Asymmetric Amination of 1,2-Diol through Borrowing Hydrogen: Synthesis of Vicinal Amino α-Tertiary Alcohol

Methods to prepare vicinal amino alcohols are important because of their presence in biologically active compounds. Despite the development of various methods for vicinal amino alcohol synthesis, C(sp3)-rich oxygen-containing β-amine compounds continue to pose great challenge. While ring-opening reaction of epoxides with amine nucleophile is the prime method for vicinal amino alcohol preparation, epoxides are highly reactive and sometimes difficult to make, resulting in drawbacks regarding selectivity of this approach. Here, we report a catalytic enantio-convergent amination of α-tertiary 1,2-diols for the efficient access to vicinal amino α-tertiary alcohols. The racemic α-tertiary 1,2-diol substrates of different alkyl/aryl or alkyl/alkyl backbone, can be converted to chiral vicinal amino α-tertiary alcohols through diphenyl phosphate-mediated RuCl3 catalysed asymmetric borrowing hydrogen (ABH) pathway. This simple ABH reaction can be scaled up to the synthesis of chiral ligands, synthetic intermediates, and other medicinally-relevant compounds. Overall, this catalytic redox-neutral procedure broadens the scope of Ru-catalysed amination of alcohols and discloses an underexplored step- and atom-economical synthetic strategy for the synthesis of vicinal amino α-tertiary alcohols and provides a practicable alternative to the present benchmark procedures.

Dynamic Kinetic Resolution Allows Control of Remote Stereochemistry in Asymmetric Hydrogen Borrowing Alkylation

A catalytic asymmetric method for the synthesis of γ-substituted ketones via hydrogen borrowing alkylation of both racemic linear precursors and 1,5-diols is described. The base mediated racemization of an intermediate cyclohexenone to facilitates a dynamic kinetic resolution, affording highly enantioenriched cyclohexanes in excellent yields, which could be further functionalized by removal of the Ph* group. DFT modelling revealed the mode of enantioinduction to be a stepwise process comprising of a hydride transfer and a coordination change to a π-allylic enolate complex with the iridium catalyst.

Universal Reagent for Mild and Stereospecific Nucleophilic Substitution of Alcohols with Amines

A user-friendly reagent for mild and general activation of alcohols towards bimolecular nucleophilic substitution (SN2) leveraging diverse nucleophiles, including primary and secondary amines is reported herein. The new ion-paired reagent discovery was based upon the putative zwitterionic betaine intermediate of the Mitsunobu reaction and enabled the one-step conversion of enantioenriched alcohols to valuable chiral C-X bonds (where X=N, C, S, O or halide). The described activating reagent has also been applied to a one-step methylation reaction using methanol and to an intermolecular amination/intramolecular cyclization sequence that generates heterocycles, such as tetrahydroisoquinolines. This work provides the first evidence by X-ray crystallography of a protonated betaine as intermediate in the Mitsunobu reaction.

Catalytic Asymmetric Synthesis of β-Amino α-Tertiary Alcohol through Borrowing Hydrogen Amination

The first enantioconvergent transition-metal-catalyzed amination of racemic α-tertiary 1,2-diols providing access to vicinal β-amino α-tertiary alcohols is disclosed. The iridium-catalyzed amination reaction proceeds through a chiral phosphoric acid-mediated borrowing hydrogen pathway with excellent yields and enantioselectivities for a range of amine nucleophiles and α-tertiary 1,2-diols. An array of β-amino α-tertiary alcohols were obtained with high yields and enantioselectivities (50 examples with up to 91% yield and up to 99% ee). These important chiral amino alcohol products can be easily converted into chiral ligands and bioactive skeletons. Mechanistic investigations proposed a dynamic kinetic resolution pathway involving imine formation and then imine reduction as the enantiodetermining step.

Desymmetrization of 1,4-Diynes by Allylic Alcohol-Triggered Redox Enyne Cycloisomerization

We report herein an unprecedented desymmetrization of 1,4-diynes via a Rh-catalyzed asymmetric redox cycloisomerization. This method adopts allylic alcohol-containing diynes and provides efficient access to multi-functional pyrrolidines and tetrahydrofurans in high to excellent stereoselectivities. Mechanistic studies highlighted an innovative catalytic pathway that differs from the classical enyne cycloisomerization and involves initiation at the allylic alcohol moiety. Diverse derivatizations of the heterocyclic products including intriguing skeletal rearrangements have also been demonstrated.

Manganese(I)-Catalyzed Enantioselective Formal Anti-Markovnikov Hydroalkoxylation of Racemic Allylic Alcohols: A Borrowing Hydrogen Access

An enantioselective manganese(I)-catalyzed formal anti-Markovnikov hydroalkoxylation of racemic allylic alcohols has been developed using a chiral N6-type macrocyclic ligand, affording a wide range of chiral γ-alkoxypropyl alcohols in high isolated yields with excellent enantioselectivities. The synthetic utility of this protocol was further proven by gram-scale synthesis of chiral γ-alkoxypropanol 3n and derivatization of chiral γ-alkoxypropanol 3a to a drug molecule, (S)-dapoxetine, for the treatment of premature ejaculation and erectile dysfunction. Mechanistic studies support that the reaction proceeds via a hydrogen-borrowing cascade reaction pathway.

Borrowing Hydrogen/Chiral Enamine Relay Catalysis Enables Diastereo- and Enantioselective β-C-H Functionalization of Alcohols

We report herein an unprecedented borrowing hydrogen/chiral enamine relay catalysis strategy that enables a highly efficient enantioselective formal β-alkylation of simple alcohols using electron-deficient alkenes and especially nitroalkenes. A variety of 1,4-difunctional products such as nitro alcohols are readily accessible in one waste-free step from feedstock alcohols in excellent levels of stereoselectivity. It is important to note that the products are formed in much higher diastereoselectivity than the enamine catalysis step alone under identical conditions, highlighting the unique advantage of cascade borrowing hydrogen catalysis in achieving high efficiency, economy, and stereoselectivity.

Dual relay Rh-/Pd-catalysis enables β-C(sp3)-H arylation of α-substituted amines

A dual relay catalytic protocol, built on reversible dehydrogenation of amines by Rh catalysis and C-H functionalisation of transient imines by Pd catalysis, is reported to enable regioselective arylation of amines at their unactivated β-C(sp3)-H bond. Notably, the new strategy is applicable to secondary anilines and N-PMP-protected primary aliphatic amines of intermediate steric demands, which is in contrast to the existing strategies that involve either free-amine-directed C-H activation for highly sterically hindered secondary aliphatic amines or steric-controlled migrative cross-coupling for unhindered N-Boc protected secondary aliphatic amines. Regioselectivity of the reaction is imposed by the electronic effects of transient imine intermediates rather than by the steric effects between specific starting materials and catalysts, thereby opening the uncharted scope of amines. In a broader sense, this study demonstrates new opportunities in dual relay catalysis involving hydrogen borrowing chemistry, previously explored in the functionalisation of alcohols, to execute otherwise challenging transformations for amines, commonly present in natural products, pharmaceuticals, biologically active molecules, and functional materials.

Asymmetric Relay Catalysis Enables Unreactive Allylic Alcohols to Participate in 1,3-Dipolar Cycloaddition of Azomethine Ylides

Current synthetic transformations occur readily with starting materials that possess both innate reactivity and steric accessibility or functional-group-oriented reactivity. However, achieving reactions with inactive feedstock substrates remains significantly challenging and normally requires cumbersome prior functional group manipulations. Herein, we report an unprecedented example of catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides with nonactivated alkenes enabled by copper/ruthenium relay catalysis. Key to the success is the temporary activation strategy initiated by oxidative dehydrogenation of inert allylic alcohols into electron-demanding reversed highly reactive enones, which triggers the ensuing Cu-catalyzed asymmetric 1,3-dipolar cycloaddition followed by reductive hydrogenation to deliver highly functionalized chiral pyrrolidines with the construction of two C-C bonds and four well-defined stereogenic centers in an atom-/step-economical and redox-neutral manner. This method features mild reaction conditions, operational simplicity, and broad substrate scope and is also characterized by formal dynamic kinetic resolution. Mechanistic studies and control experiments supported a typical borrowing-hydrogen cascade orthogonally merged with 1,3-dipolar cycloaddition and revealed that the superiority and reliability of relay catalysis are enabled by the controlled release of highly reactive but unstable enones to impede the undesired polymerization. It should be noted that up to four stereoisomers of the challenging and otherwise inaccessible pyrrolidines and cyclobutanes could be readily prepared through concise late-stage elaborations.

Employing Ammonia for the Synthesis of Primary Amines: Recent Achievements over Heterogeneous Catalysts

Primary amines represent highly privileged chemicals for synthesis of polymers, pharmaceuticals, agrochemicals, coatings, etc. Consequently, the development of efficient and green methodologies for the production of primary amines are of great importance in chemical industry. Owing to the advantages of low cost and ease in availability, ammonia is considered as a feasible nitrogen source for synthesis of N-containing compounds. Thus, the efficient transformation of ammonia into primary amines has received much attention. In this review, the commonly applied synthetic routes to produce primary amines from ammonia were summarized, including the reductive amination of carbonyl compounds, the hydrogen transfer amination of alcohols, the hydroamination of olefins and the arylation with ammonia, in which the catalytic performance of the recent heterogeneous catalysts is discussed. Additionally, various strategies to modulate the surface properties of catalysts are outlined in conjunction with the analysis of reaction mechanism. Particularly, the amination of the biomass-derived substrates is highlighted, which could provide competitive advantages in chemical industry and stimulate the development of sustainable catalysis in the future. Ultimately, perspectives into the challenges and opportunities for synthesis of primary amines with ammonia as N-resource are discussed.

Stereodivergent assembly of δ-valerolactones with an azaarene-containing quaternary stereocenter enabled by Cu/Ru relay catalysis

Developing methodologies for the expedient construction of biologically important δ-valerolactones bearing a privileged azaarene moiety and a sterically congested all-carbon quaternary stereocenter is important and full of challenges. We present herein a novel multicatalytic strategy for the stereodivergent synthesis of highly functionalized chiral δ-valerolactones bearing 1,4-nonadjacent quaternary/tertiary stereocenters by orthogonally merging borrowing hydrogen and Michael addition between α-azaaryl acetates and allylic alcohols followed by lactonization in a one-pot manner. Enabled by Cu/Ru relay catalysis, this cascade protocol offers the advantages of atom/step economy, redox-neutrality, mild reaction conditions, and broad substrate tolerance. Scale-up experiments and synthetic transformations further demonstrated the potential for synthetic applications. Mechanistic experiments support the envisioned bimetallic relay catalytic mechanism, and the key role of Cs2CO3 in promoting lactonization was also revealed.

Terpenylation of Ketones and a Secondary Alcohol under Hydrogen-Borrowing Manganese Catalysis

An Earth-abundant Mn-PNP pincer complex-catalyzed terpenylation of cyclic and acyclic ketones and secondary alcohol 1-phenylethanol using isoprenoid derivatives prenol, nerol, phytol, solanesol, and E-farnesol as allyl surrogates is reported. The C-C coupling reactions are green and atom-economic, proceeding via dehydrogenation of alcohols following a hydrogen autotransfer methodology aided by metal-ligand cooperation.

Iridium-Catalyzed Enantioconvergent Construction of Piperidines and Tetrahydroisoquinolines from Racemic 1,5-Diols

We report herein a one-step synthesis of valuable enantioenriched piperidines and tetrahydroisoquinolines from readily available racemic 1,5-diols. Key to the success is the development of new iridacycle catalysts that enable efficient redox-neutral construction of two C-N bonds between diols and amines in an enantioconvergent fashion. Mechanistic studies identified an intriguing preferential oxidation of secondary versus primary alcohol in the diol substrate by the iridacycle catalyst, which set a challenging intermolecular amination of aryl-alkyl-substituted alcohol as the enantiodetermining step for this catalytic N-heterocycle synthesis. Application of this catalytic method to the preparation of important drugs and bioactive compounds is also demonstrated.

Dynamic Asymmetric Diamination of Allylic Alcohols through Borrowing Hydrogen Catalysis: Diastereo-Divergent Synthesis of Tetrahydrobenzodiazepines

We present herein a catalytic enantioconvergent diamination of racemic allylic alcohols with the construction of two C-N bonds and 1,3-nonadjacent stereocenters. This iridium/chiral phosphoric acid cooperative catalytic system operates through an atom-economical borrowing hydrogen amination/aza-Michael cascade, and converts readily available phenylenediamines and racemic allylic alcohols to 1,5-tetrahydrobenzodiazepines in high enantioselectivity. An intriguing solvent-dependent switch of diastereoselectivity was also observed. Mechanistic studies suggested a dynamic kinetic resolution process involving racemization through a reversible Michael addition, making the last step of asymmetric imine reduction the enantiodetermining step of this cascade process.

Pnictogen and Chalcogen Salts as Alkylating Agents

Alkylation reactions and their products are considered crucial in various contexts. Synthetically, the alkylation of a nucleophile is usually promoted using hazardous alkyl halides. Here, we aim to highlight the potential of pnictogen (ammonium or phosphonium) and chalcogen salts (sulfonium, selenonium, and telluronium) to function as alkylating agents. These compounds can be considered as non-volatile electrophilic alkyl reservoirs. We will center our discussion on the strategies developed in recent years to expand the synthetic utility of these salts in terms of transferable alkyl groups, substrate scope, and product selectivity.

Multifunctionalization of Alkenyl Alcohols via a Sequential Relay Process

Aryl-substituted aliphatic amines are widely recognized as immensely valuable molecules. Consequently, the development of practical strategies for the construction of these molecules becomes increasingly urgent and critical. Here, we have successfully achieved multifunctionalization reactions of alkenyl alcohols in a sequential relay process, which enables transformation patterns of arylamination, deuterated arylamination, and methylenated arylamination to the easy access of multifarious arylalkylamines. Notably, a novel functionalization mode for carbonyl groups has been developed to facilitate the processes of deuterium incorporation and methylene introduction, thereby providing new means for the diverse transformations of carbonyl groups. This methodology displays a wide tolerance toward functional groups, while also exhibiting good applicability across various skeletal structures of alkenols and amines.

Iron-Catalyzed Transfer Hydrogenation of Allylic Alcohols with Isopropanol

Herein, we report an iron-catalyzed transfer hydrogenation of allylic alcohols. The operationally simple protocol employs a well-defined bench stable (cyclopentadienone)iron(0) carbonyl complex as a precatalyst in combination with K2CO3 (4 mol %) and isopropanol as the hydrogen donor. A diverse range of allylic alcohols undergo transfer hydrogenation to form the corresponding alcohols in good yields (33 examples, ≤83% isolated yield). The scope and limitations of the method have been investigated, and experiments that shed light on the reaction mechanism have been conducted.

Manganese-catalyzed cyclopropanation of allylic alcohols with sulfones

Cyclopropanes are among the most important structural units in natural products, pharmaceuticals, and agrochemicals. Herein, we report a manganese-catalyzed cyclopropanation of allylic alcohols with sulfones as carbene alternative precursors via a borrowing hydrogen strategy under mild conditions. Various allylic alcohols and arylmethyl trifluoromethyl sulfones work efficiently in this borrowing hydrogen transformation and thereby deliver the corresponding cyclopropylmethanol products in 58% to 99% yields. Importantly, a major benefit of this transformation is that the versatile free alcohol moiety is retained in the resultant products, which can undergo a wide range of downstream transformations to provide access to a series of functional molecules. Mechanistic studies support a sequential reaction mechanism that involves catalytic dehydrogenation, Michael addition, cyclization, and catalytic hydrogenation.

Iron- and Organo-Catalyzed Borrowing Hydrogen for the Stereoselective Construction of Tetrahydropyrans

Stereocontrolled oxa-Michael additions are challenging, given the high reversibility of the process, which ultimately leads to racemization of the newly formed stereocenters. When iron-catalyzed borrowing hydrogen from allylic alcohols was combined with a stereocontrolled organocatalytic oxa-Michael addition, a wide array of chiral tetrahydropyrans were efficiently prepared. The reaction could be performed in a diastereoselective manner from pre-existing stereocenters or enantioselectively from achiral substrates. The key to success was the reactivity of the iron complex, which was selective for allylic alcohol dehydrogenation and irreversibly led the reaction to the final product.

Copper/ruthenium relay catalysis enables 1,6-double chiral inductions with stereodivergence

The dual catalysis strategy is an efficient and powerful tool to fulfill the stereodivergent synthesis of stereoisomeric products from the same set of starting materials. Great attention has been given to the construction of chiral compounds with two contiguous stereocenters. However, the synthesis of two remote noncontiguous stereocenters is more challenging and is less developed, despite the high demand for synthetic tactics. We herein developed an unprecedented example of the stereodivergent preparation of synthetically useful and biologically important chiral ζ-hydroxy amino ester derivatives containing remote 1,6-noncontiguous stereocenters and a unique β,γ-unsaturation moiety. This cascade dehydrogenation/1,6-Michael addition/hydrogenation protocol between readily-available ketoimine esters and racemic branched dienyl carbinols was rationally realized with bimetallic copper/ruthenium relay catalysis. The key features of the process were atom economy, step economy, and redox-neutrality. All four stereoisomers of chiral ζ-hydroxy amino ester derivatives were easily achieved by the orthogonal permutations of a chiral copper catalyst and chiral ruthenium catalyst. Importantly, a much more challenging stereodivergent synthesis of all eight stereoisomers of chiral peptide products containing three remote stereocenters was accomplished with excellent results through the cooperation of two chiral catalyst pairs and substrate enantiomers.

Ruthenium Complexes with NNN-Pincer Ligands for N-Methylation of Amines Using Methanol

A series of ruthenium complexes (Ru1-Ru4) bearing new NNN-pincer ligands were synthesized in 58-78% yields. All of the complexes are air and moisture stable and were characterized by IR, NMR, and high-resolution mass spectra (HRMS). In addition, the structures of Ru1-Ru3 were confirmed by X-ray crystallographic analysis. These Ru(II) complexes exhibited high catalytic efficiency and broad functional group tolerance in the N-methylation reaction of amines using CH3OH as both the C1 source and solvent. Experimental results indicated that the electronic effect of the substituents on the ligands considerably affects the catalytic reactivity of the complexes in which Ru3 bearing an electron-donating OMe group showed the highest activity. Deuterium labeling and control experiments suggested that the dehydrogenation of methanol to generate ruthenium hydride species was the rate-determining step in the reaction. Furthermore, this protocol also provided a ready approach to versatile trideuterated N-methylamines under mild conditions using CD3OD as a deuterated methylating agent.

Enantioconvergent synthesis of chiral fluorenols from racemic secondary alcohols via Pd(ii)/chiral norbornene cooperative catalysis

An efficient protocol for the asymmetric synthesis of fluorenols has been developed through an enantioconvergent process enabled by Pd(ii)/chiral norbornene cooperative catalysis. This approach allows facile access to diverse functionalized chiral fluorenols with constantly excellent enantioselectivities, applying readily available racemic secondary ortho-bromobenzyl alcohols and aryl iodides as the starting materials.

Biocatalytic Hydrogen-Borrowing Cascade in Organic Synthesis

Biocatalytic hydrogen borrowing represents an environmentally friendly and highly efficient synthetic method. This innovative approach involves converting various substrates into high-value-added products, typically via a one-pot, two/three-step sequence encompassing dehydrogenation (intermediate transformation) and hydrogenation processes employing the hydride shuffling between NAD(P)+ and NAD(P)H. Represented key transformations in hydrogen borrowing include stereoisomer conversion within alcohols, conversion between alcohols and amines, conversion of allylic alcohols to saturated carbonyl counterparts, and α,β-unsaturated aldehydes to saturated carboxylic acids, etc. The direct transformation methodology and environmentally benign characteristics of hydrogen borrowing have contributed to its advancements in fine chemical synthesis or drug developments. Over the past decades, the hydrogen borrowing strategy in biocatalysis has led to the creation of diverse catalytic systems, demonstrating substantial potential for straightforward synthesis as well as asymmetric transformations. This perspective serves as a detailed exposition of the recent advancements in biocatalytic reactions employing the hydrogen borrowing strategy. It provides insights into the potential of this approach for future development, shedding light on its promising prospects in the field of biocatalysis.

Manganese-Catalyzed Mono-N-Methylation of Aliphatic Primary Amines without the Requirement of External High-Hydrogen Pressure

The synthesis of mono-N-methylated aliphatic primary amines has traditionally been challenging, requiring noble metal catalysts and high-pressure H2 for achieving satisfactory yields and selectivity. Herein, we developed an approach for the selective coupling of methanol and aliphatic primary amines, without high-pressure hydrogen, using a manganese-based catalyst. Remarkably, up to 98 % yields with broad substrate scope were achieved at low catalyst loadings. Notably, due to the weak base-catalyzed alcoholysis of formamide intermediates, our novel protocol not only obviates the addition of high-pressure H2 but also prevents side secondary N-methylation, supported by control experiments and density functional theory calculations.

Preparation of a novel cadmium-containing coordination polymer and catalytic application in the synthesis of N-alkylated aminoquinoline derivatives via the borrowing hydrogen approach

Herein, we report an efficient and straightforward approach for the synthesis of N-alkylated aminoquinoline derivatives by recyclable Cd-containing coordination polymer-catalyzed reactions of aminoquinolines with primary alcohols via the borrowing hydrogen strategy. In this work, a new type of coordination polymer [Cd(CIA)(phen)2(H2O)]n was successfully designed and fabricated. The molecular structure was corroborated by single-crystal X-ray diffraction and fully characterized by PXRD, FT-IR, TGA, and XPS. Importantly, this polymer revealed high catalytic activity for the N-alkylation reaction of 2-aminoquinoline and 8-aminoquinoline with inexpensive and low-toxicity alcohols as alkylating agents in excellent yields up to 95%. Interestingly, the present synthetic protocol was successfully applied for the gram-level synthesis of several biologically active compounds. In addition, several control reactions were carried out to investigate the possible mechanisms of this transformation. Finally, recycling experiments indicated that the cadmium coordination polymer showed good recovery performance for borrowing hydrogen reactions.

Copper/Ruthenium Relay Catalysis for Stereodivergent Access to δ-Hydroxy α-Amino Acids and Small Peptides

An atom- and step-economical and redox-neutral cascade reaction enabled by asymmetric bimetallic relay catalysis by merging a ruthenium-catalyzed asymmetric borrowing-hydrogen reaction with copper-catalyzed asymmetric Michael addition has been realized. A variety of highly functionalized 2-amino-5-hydroxyvaleric acid esters or peptides bearing 1,4-non-adjacent stereogenic centers have been prepared in high yields with excellent enantio- and diastereoselectivity. Judicious selection and rational modification of the Ru catalysts with careful tuning of the reaction conditions played a pivotal role in stereoselectivity control as well as attenuating undesired α-epimerization, thus enabling a full complement of all four stereoisomers that were otherwise inaccessible in previous work. Concise asymmetric stereodivergent synthesis of the key intermediates for biologically important chiral molecules further showcases the synthetic utility of this methodology.

Borrowing Hydrogen β-Phosphinomethylation of Alcohols Using Methanol as C1 Source by Pincer Manganese Complex

Herein, we report a manganese-catalyzed three-component coupling of β-H containing alcohols, methanol, and phosphines for the synthesis of γ-hydroxy phosphines via a borrowing hydrogen strategy. In this development, methanol serves as a sustainable C1 source. A variety of aromatic and aliphatic substituted alcohols and phosphines could undergo the dehydrogenative cross-coupling process efficiently and deliver the corresponding β-phosphinomethylated alcohol products in moderate to good yields. Mechanistic studies suggest that this transformation proceeds in a sequential manner including catalytic dehydrogenation, aldol condensation, Michael addition, and catalytic hydrogenation.