Kinetic Resolution Research Articles

Enantioselective Intramolecular Hydroacylation of Alkynes by Rhodium Catalysis through Dynamic Kinetic Resolution

AbstractRhodium‐catalyzed enantioselective hydroacylation of racemic alkynals having a substituent at the α‐position of the carbonyl group is described. This reaction can be applied for the wide range of substrates (22 examples), and mechanistic studies revealed that a dynamic kinetic resolution (DKR) process occurs during the hydroacylation, giving various cyclic ketones in 47–93% yields with 59:41 to 97:3 er from racemic starting materials.

Kinetic resolution of thermal runaway for lithium-ion batteries: A Gaussian surrogate-assisted separate optimization approach

Accurate kinetic resolution of thermal runaway (TR) for lithium-ion batteries (LIBs) plays a central role in battery safety design and early warning. However, simultaneous extraction of the number and kinetic parameters of TR reactions from multi-peak overlapping differential scanning calorimetry (DSC) profiles is a complicated nonlinear programming optimization problem. A Gaussian surrogate-assisted separate optimization framework is proposed to address the kinetic resolution problem. First, an offline equivalent kinetic database, based on the geometric similarity of heat flow peaks and Gaussian functions, is designed to provide initial parameter estimations for multiple reactions. Second, an adaptive range division method, based on priori local extrema, is proposed to divide the DSC profile into separate ranges of fitting (ROF) to assist the key mechanism selection. Third, divisional kinetic resolution is performed for each ROF where kinetic models initialized by the above database are utilized to fit sub-range profiles and then potential solutions are searched based on a posteriori error-based criterion. Finally, Bayesian information criterion is utilized for the optimal solution selection among the combinations of potential solutions for multiple ROFs. The proposed framework is validated through experimental data from the DSC tests of types of LIBs. The results illustrate the applicability and efficiency of the proposed framework.

Nickel‐Catalyzed Tunable Enantioconvergence and Kinetic Resolution in the Coupling of Tertiary Cyclobutenols with Arylboroxines

AbstractWe report that a nickel catalyst system with a modified 1,1′‐spirobiindane‐7,7′‐diol‐phosphoramidite (SPINOL) as the chiral ligand can enable the coupling of tertiary cyclobutenols and arylboroxines in an enantioconvergent manner, providing cyclobutenes with an all‐carbon quaternary stereocenter in good yields (up to 84 % yield) with excellent enantioselectivities (up to >99 % ee). Moreover, the catalytic system can be applied in the kinetic resolution of cyclobutenols under slightly modified conditions, giving enantioenriched tertiary cyclobutenols with an s factor of up to >200. The reaction uses free hydroxyl groups as the leaving group without additional activation while the strained ring remains untouched. Preliminary mechanistic studies reveal that the inherent discrepant reactivity of the two enantiomers is the key to the controllable enantioconvergent and kinetic resolution process.

Nickel-Catalyzed Tunable Enantioconvergence and Kinetic Resolution in the Coupling of Tertiary Cyclobutenols with Arylboroxines.

We report that a nickel catalyst system with a modified 1,1'-spirobiindane-7,7'-diol-phosphoramidite (SPINOL) as the chiral ligand can enable the coupling of tertiary cyclobutenols and arylboroxines in an enantioconvergent manner, providing cyclobutenes with an all-carbon quaternary stereocenter in good yields (up to 84 % yield) with excellent enantioselectivities (up to >99 % ee). Moreover, the catalytic system can be applied in the kinetic resolution of cyclobutenols under slightly modified conditions, giving enantioenriched tertiary cyclobutenols with an s factor of up to >200. The reaction uses free hydroxyl groups as the leaving group without additional activation while the strained ring remains untouched. Preliminary mechanistic studies reveal that the inherent discrepant reactivity of the two enantiomers is the key to the controllable enantioconvergent and kinetic resolution process.

Enantioselective Sequential Catalytic Arylation-Fukuyama Cross-coupling of 1,1-Biszincioalkane Linchpins.

1,1-Bis(iodozincio)alkanes are used as dinucleophilic linchpins in an enantioselective double cross-coupling reaction sequence involving aryl iodides and then thioesters. The two catalytic C-C bond-forming reactions are achieved in the same pot through two distinct palladium-based catalytic systems: a first non-enantioselective one delivering configurationally labile secondary benzylzinc species from an achiral precursor, and a second enantioconvergent one that operates a highly efficient dynamic kinetic resolution of the racemic intermediates. This strategy, new in the area of asymmetric synthesis through two consecutive electrophilic substitution reactions of geminated C(sp3 )-organodimetallics, provides useful methodology to access in a modular fashion acyclic α-disubstituted ketone products with very high enantiomeric purity.

Nickel-Catalyzed Kinetic Resolution of Racemic Unactivated Alkenes via Enantio-, Diastereo-, and Regioselective Hydroamination.

Kinetic resolution is a powerful strategy for the isolation of enantioenriched compounds from racemic mixtures, and the development of selective catalytic processes is an active area of research. Here, we present a nickel-catalyzed kinetic resolution of racemic α-substituted unconjugated carbonyl alkenes via the enantio-, diastereo-, and regioselective hydroamination. This protocol affords both chiral α-substituted butenamides and syn-β2,3 -amino acid derivatives with high enantiomeric purity (up to 99 % ee) and selectivity factor up to >684. The key to the excellent kinetic resolution efficiency is the distinctive architecture of the chiral nickel complex, which enables successful resolution and enantioselective C-N bond construction. Mechanistic investigations reveal that the unique structure of the chiral ligand facilitates a rapid migratory insertion step with one enantiomer. This strategy provides a practical and versatile approach to prepare a wide range of chiral compounds.

Nickel‐Catalyzed Kinetic Resolution of Racemic Unactivated Alkenes via Enantio‐, Diastereo‐, and Regioselective Hydroamination

AbstractKinetic resolution is a powerful strategy for the isolation of enantioenriched compounds from racemic mixtures, and the development of selective catalytic processes is an active area of research. Here, we present a nickel‐catalyzed kinetic resolution of racemic α‐substituted unconjugated carbonyl alkenes via the enantio‐, diastereo‐, and regioselective hydroamination. This protocol affords both chiral α‐substituted butenamides and syn‐β2,3‐amino acid derivatives with high enantiomeric purity (up to 99 % ee) and selectivity factor up to >684. The key to the excellent kinetic resolution efficiency is the distinctive architecture of the chiral nickel complex, which enables successful resolution and enantioselective C−N bond construction. Mechanistic investigations reveal that the unique structure of the chiral ligand facilitates a rapid migratory insertion step with one enantiomer. This strategy provides a practical and versatile approach to prepare a wide range of chiral compounds.

Kinetic Resolution of 2-Aryldihydroquinolines Using Lithiation - Synthesis of Chiral 1,2- and 1,4-Dihydroquinolines.

Highly enantiomerically enriched dihydrohydroquinolines were prepared in two steps from quinoline. Addition of aryllithiums to quinoline with tert-butoxycarbonyl (Boc) protection gave N-Boc-2-aryl-1,2-dihydroquinolines. These were treated with n-butyllithium and electrophilic trapping occurred exclusively at C-4 of the dihydroquinoline, a result supported by DFT studies. Variable temperature NMR spectroscopy gave kinetic data for the barrier to rotation of the carbonyl group (ΔG≠ ≈49 kJ mol-1 , 195 K). Lithiation using the diamine sparteine allowed kinetic resolutions with high enantioselectivities (enantiomer ratio up to 99 : 1). The enantioenriched 1,2-dihydroquinolines could be converted to 1,4-dihydroquinolines with retention of stereochemistry. Further functionalisation led to trisubstituted products. Reduction provided enantioenriched tetrahydroquinolines, whereas acid-promoted removal of Boc led to quinolines, and this was applied to a synthesis of the antimalarial compound M5717.

Cu‐Catalyzed Asymmetric Kinetic Boron Conjugate Addition of γ‐Substituted α,β‐Unsaturated γ‐Lactams

AbstractChiral α,β‐unsaturated γ‐lactams bearing simple γ‐ substituents are found in biologically active molecules and natural products, however, their synthesis still remains difficult. Herein, we report an efficient kinetic resolution (KR) of γ‐substituted α,β‐unsaturated γ‐lactams via a Cu‐catalyzed asymmetric boron conjugate addition, which also leads to the efficient synthesis of chiral β‐hydroxy‐γ‐lactams with β,γ‐stereogenic carbon centers. The KR proceeded smoothly with a wide range of γ‐alkyl or aryl substituted substrates including those bearing aromatic heterocycles and different N‐protected substrates in up to 347 of s value. Their highly versatile transformations, synthetic utility in biologically active molecules, and inhibitory activities against cisplatin‐sensitive ovarian cancer cell A2780 have also been demonstrated. Differing from the well‐known mechanism involving Cu−B species in Cu‐catalyzed boron conjugate additions, our mechanistic studies using density functional theory (DFT) calculations and experiments indicate that a Lewis acid CuI‐catalyzed mechanism is the likely pathway in the catalytic reaction.

Cu-Catalyzed Asymmetric Kinetic Boron Conjugate Addition of γ-Substituted α,β-Unsaturated γ-Lactams.

Chiral α,β-unsaturated γ-lactams bearing simple γ- substituents are found in biologically active molecules and natural products, however, their synthesis still remains difficult. Herein, we report an efficient kinetic resolution (KR) of γ-substituted α,β-unsaturated γ-lactams via a Cu-catalyzed asymmetric boron conjugate addition, which also leads to the efficient synthesis of chiral β-hydroxy-γ-lactams with β,γ-stereogenic carbon centers. The KR proceeded smoothly with a wide range of γ-alkyl or aryl substituted substrates including those bearing aromatic heterocycles and different N-protected substrates in up to 347 of s value. Their highly versatile transformations, synthetic utility in biologically active molecules, and inhibitory activities against cisplatin-sensitive ovarian cancer cell A2780 have also been demonstrated. Differing from the well-known mechanism involving Cu-B species in Cu-catalyzed boron conjugate additions, our mechanistic studies using density functional theory (DFT) calculations and experiments indicate that a Lewis acid CuI -catalyzed mechanism is the likely pathway in the catalytic reaction.

Kinetic Resolution of trans-2,3-Aziridinyl Alcohols via Hydroxyl Directed Regio- and Enantioselective Ring Opening Reactions

An efficient kinetic resolution of racemic trans-2,3-aziridinyl alcohols is established via zinc catalyzed ring opening reactions with various amines as the nucleophiles. The directing effect of the hydroxyl group and the precise enantiodiscrimination by dinuclear zinc cooperative catalyst are the keys to success of high regioselectivity and enantioselectivity. A range of enantioenriched vicinal diamines and trans-2,3-aziridinyl alcohols were obtained in good yields with excellent ee values. To the best of our knowledge, this is the first example of directed enantioselective nucleophilic ring opening reactions of 2,3-aziridinyl alcohols.

A Common C2 -Symmetric 2,2'-Biphenol Building Block and its Application in the Synthesis of (+)-di-epi-Gonytolide A.

A variety of biaryl polyketides exhibit remarkable bioactivities. However, their synthetic accessibility is often challenging. Herein, the enantioselective preparation and synthetic application of an axially chiral 2,2'-biphenol building block is outlined that represents a common motif of these intriguing natural products. Based on the highly regioselective and scalable bromination of a phenol precursor, a coupling process by Lipshutz cuprate oxidation was developed. A copper-mediated deracemization strategy proved to be superior to derivatization or kinetic resolution approaches. Key steps in the overall building block synthesis were rationalized through DFT studies. Utilizing the 2,2'-biphenol, a highly diastereoselective five step synthesis of formerly unknown (+)-di-epi-gonytolide A was developed, thus showcasing the building block's general potential for the synthesis of natural products and their derivatives. En route, the first enantioselective construction of a chromone dimer intermediate was established.

Modification of the properties of the metagenomic lipase LipC12 by engineering of the hydrophobic cavity

Kinetic resolution of racemates with lipases is the preferred method for producing bioactive compounds. One strategy for obtaining highly enantioselective lipases that are stable in the organic media that are often used in these reactions is to improve existing lipases by protein engineering. In this work, we engineered the lipase LipC12, which has good stability in organic media, but only moderate enantioselectivity. Molecular docking with LipC12 identified V261 as a key position influencing, first, enantioselectivity in the transesterification of (RS)-1-phenylethanol and, second, activity in the hydrolysis of p-nitrophenyl octanoate. Variants were then obtained by site-directed mutagenesis, expressed in Escherichia coli, and their performance in these reactions was evaluated. Enzymes immobilized on Immobead 150 were used in the transesterification while free enzyme was used in the hydrolysis reaction. It was not possible to increase the hydrolytic activity and enantioselectivity simultaneously: some variants had increased enantioselectivity but lower hydrolytic activity, and others had increased hydrolytic activity but lower enantioselectivity. The best result for enantioselectivity was obtained for LipC12V261Q, with an increase of the E-value (for (R)-1-phenylethanol) from 46 to 110, however, its hydrolytic activity decreased 4-fold in comparison to LipC12wt. The highest hydrolytic activity was obtained for LipC12V261F, with a value almost 6-fold higher than that of LipC12wt. This variant also had an inverted enantiopreference (i.e. for (S)-1-phenylethanol), but with a very low E-value of only 4.

Rhodium-Catalyzed Asymmetric Conjugate Addition to γ-Substituted α,β-Unsaturated γ-Lactams through Dynamic Kinetic Resolution: Asymmetric Synthesis of trans-β,γ-Disubstituted γ-Lactams

The reaction of racemic γ-substituted α,β-unsaturated γ-lactams rac-1 with arylboron reagents 2 in the presence of a chiral diene L1a–rhodium catalyst under basic conditions (3.0 equiv of NEt3) gave high yields of β,γ-disubstituted trans-γ-lactams 3 with both high diastereo- and enantioselectivity. Fast racemization of 1 by way of a dienolate generated with the base followed by kinetic resolution of 1 with the chiral rhodium catalyst realized this highly efficient dynamic kinetic resolution. The synthetic utility of the present method is demonstrated by the synthesis of key intermediates to biologically active compounds.

Differentiating the Allyl and Propargyl Groups on α‐Quaternary Carboxylic Acids via Chiral Bifunctional Sulfide‐Catalyzed Kinetic Resolution

AbstractCatalytic kinetic resolution of racemic organic compounds is a reliable method to enantioselectively prepare important chiral molecules. Substrates for the kinetic resolution, however, generally required significantly different substituents at a chiral center. Catalytic kinetic resolution of racemic molecules possessing two similar substituents at a chiral center has remained a formidable challenge. In this context, we became interested in the catalytic kinetic resolution of racemic compounds bearing both allyl and propargyl groups, which are similar but useful substituents, at a chiral center. Herein, we report a kinetic resolution of α‐allyl‐α‐propargyl carboxylic acids bearing an all‐carbon quaternary stereocenter via chiral bifunctional sulfide‐catalyzed bromolactonization. The synthetic utility of the resultant optically active compounds obtained via kinetic resolution was also demonstrated.magnified image

Synthesis of Functionalized Spirooxindole Polycycles: Use of Cyclic 1,3-Diones as Reactants or as Condition-Tuning Molecules

AbstractThis account describes the strategies for the synthesis of functionalized spirooxindole polycycles, including enantiomerically enriched forms, that we have developed and reported. The syntheses of these complex molecules were accomplished in a few steps starting from relatively simple oxindole derivatives and other reactants. Organocatalytic reactions involved in kinetic resolution or in dynamic kinetic transformation led to the formation of products with high diastereo- and/or enantioselectivities. Cyclic 1,3-diones, such as 1,3-cyclohexanedione, were used as reactants to provide two reaction sites for the construction of polycyclic ring systems. To tune the reaction conditions, 2-methyl-1,3-cyclohexanedione was employed. The developed methods enabled the synthesis of complex functionalized spirooxindole polycycles bearing up to seven stereogenic centers, and will be useful for the synthesis of potentially bioactive molecules.1 Introduction2 Formal (4+1) Cycloaddition and Enantioselective Michael/Henry Cascade Reactions3 Dynamic Stereoselective Aldol/Oxacyclization Cascade Reactions4 Dynamic Kinetic Asymmetric Transformation: Diastereo- and Enantioconvergent Michael/Henry Reactions5 Dimerization Reactions6 Conclusion

Engineered Biocatalysts for Enantioselective Reductive Aminations of Cyclic Secondary Amines

AbstractReductive aminases (RedAms) have recently emerged as promising biocatalysts for the synthesis of chiral secondary amines by coupling primary amines with aldehydes/ketones. However, access to tertiary amines remains more problematic, particularly when coupling ketones with secondary amines. Here we show that the scope of these enzymes can be extended to allow selective reductive aminations of cyclic secondary amines, such as piperidines and morpholines, with both aldehydes and ketones. These biotransformations provide access to important motifs found in active pharmaceutical ingredients and other bioactive molecules. RedAm‐361, discovered from a metagenomic library, was engineered via directed evolution to allow efficient coupling of cyclic amines with carbonyl partners, including dynamic kinetic resolutions of α‐functionalized aldehydes and enantioselective amination of ketones. These RedAms now serve as valuable scaffolds for the engineering of industrial biocatalysts to produce key pharmaceutical intermediates.

Polyethyleneimine-MOF composite as a support for immobilization of lipase with enhanced activity in kinetic resolution

Lipase PS from Pseudomonas cepacia was steadily immobilized on a new support prepared with metal-organic framework (MOF) and polyethyleneimine (PEI) through a PEI-boosted strategy (PS@MOF-5-PEI). Evaluated by the enantioselective transesterification reaction of racemic 1-(4-(trifluoromethyl) phenyl) ethanol (TFMP) with vinyl acetate, PS@MOF-5-PEI expressed more than 10 times of increase in specific activity (U/mg protein) compared with free lipase PS. PS@MOF-5-PEI had an enhanced enzyme-substrate affinity and catalytic efficiency than free lipase PS, as supported by a lower apparent Km value (7.3 vs 11.3 mM) and an increased Vmax/Km value (0.38 vs 0.05 min−1), respectively. Under the optimal conditions involving 45 °C, substrate ratio of 1:18, enzyme dosage of 20 mg and reaction time of 60 min, the ees of 99.8% and c of 50.1% for kinetic resolution of TFMP enantiomers were achieved with PS@MOF-5-PEI, which can be recycled for 10 times without significant loss in activity and with enantioselectivity well maintained.

Hydrogen-Bonding Ability of Noyori-Ikariya Catalysts Enables Stereoselective Access to CF3-Substituted syn-1,2-Diols via Dynamic Kinetic Resolution.

Stereopure CF3-substituted syn-1,2-diols were prepared via the reductive dynamic kinetic resolution of the corresponding racemic α-hydroxyketones in HCO2H/Et3N. (Het)aryl, benzyl, vinyl, and alkyl ketones are tolerated, delivering products with ≥95% ee and ≥87:13 syn/anti. This methodology offers rapid access to stereopure bioactive molecules. Furthermore, DFT calculations for three types of Noyori-Ikariya ruthenium catalysts were performed to show their general ability of directing stereoselectivity via the hydrogen bond acceptor SO2 region and CH/π interactions.

Chiral Boro‐Phosphate Catalyzed Asymmetric Transfer Hydrogenation of 1‐Enal Substituted 2‐Naphthols: Access to Axially Chiral Styrene‐Type Allylalcohols

AbstractHerein, we present a chiral boro‐phosphate catalyzed atroposelective asymmetric transfer hydrogenation method, leading to a family of axially chiral styrene‐type allylalcohols. This dynamic kinetic resolution approach portrays simple procedure, mild conditions and good enantiocontrol (51–95% ee), thus providing an important alternative to assemble the challenging atropisomeric aryl‐acyclic alkene scaffolds.magnified image