Efficient Kinetic Resolution Research Articles

Synthesis of Enantioenriched (Z)-Disubstituted Allylic Alcohols via Ru-Catalyzed Selective Dehydrogenation.

A highly efficient kinetic resolution of allylic alcohols with Z/E mixtures was achieved via Ru-catalyzed selective dehydrogenation. Not only allylic alcohols were obtained with pure Z-geometry, but the corresponding selectivity factors rank among the few highest for kinetic resolution reported in the literature.

Enantioselective Synthesis of cis‐Decalins by Merging the Birch Reduction and Inverse‐Electron‐Demand Diels–Alder Reaction

AbstractHerein, we show that the combination of the Birch reduction of readily available anisole derivatives and the catalytic asymmetric inverse‐electron‐demand Diels–Alder reaction of 2‐pyrones can serve as a powerful platform for the diverse synthesis of synthetically important cis‐decalin scaffolds. Enabled by a well‐modified chiral bis(oxazoline) ligand/CuII complex, a wide range of polysubstituted cis‐decalin scaffolds with up to six contiguous stereocenters were generated efficiently. The synthetic potential of this method is demonstrated by the concise synthesis of the sesquiterpene (+)‐occidentalol and a key intermediate for seven triterpenes. Mechanistic studies suggest the 1,3‐cyclohexadienes formed in situ are the key intermediates, and efficient kinetic resolution occurs when C2‐ and/or C3‐substituted 1,4‐cyclohexadienes are utilized as substrates. DFT calculations elucidated that the Diels–Alder reaction proceeds in a stepwise fashion and revealed the origins of the stereoselectivities.

Asymmetric Metathesis Dimerization/Kinetic Resolution of Racemic Planar-Chiral Vinylphosphaferrocenes

Asymmetric metathesis dimerization (AMD) reactions of a series of racemic planar-chiral 2-vinylphosphaferrocenes (rac-1) were examined in the presence of a chiral molybdenum-alkylidene precatalyst. The reactions proceeded in a highly enantio- and diastereoselective fashion to realize the efficient kinetic resolution (KR) of the racemic substrates. The AMD/KR reaction of rac-1a showed excellent diastereoselectivity (chiral-2a/meso-2a = >98/<2) to provide (E)-(S,S)-2a of >99% ee in 38% yield together with unreacted recovered (R)-1a of 63% ee in 58% yield. The selectivity factor (krel) of this reaction was estimated to be 1.5 × 103 based on a second-order equation. In all the cases examined, the dimerized products, chiral-2, were obtained in >98% ee even with near 50% conversions (i.e., close to the complete consumption of the more reactive enantiomers in rac-1) thanks to the outstanding enantioselectivity.

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.

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.

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.

Catalytic Asymmetric Hydrophosphinylation of 2‐Vinylazaarenes to Access P‐Chiral 2‐Azaaryl‐Ethylphosphine Oxides

AbstractA chiral Brønsted acid‐catalysed asymmetric hydrophosphinylation of 2‐vinylazaarenes by secondary phosphine oxides is described. A variety of P‐chiral 2‐azaaryl‐ethylphosphine oxides are synthesized with high yields and ees, of which both the substituents of phosphines and azaarenes can be flexibly modulated, underscoring an exceptionally broad scope of substrates. These adducts are valuable to asymmetric metal catalysis since the resultant P‐chiral tertiary phosphines from the reduction of them are verified as a kind of effective C1‐symmetric chiral 1,5‐hybrid P,N‐ligands. Importantly, this catalysis platform enables the generic and efficient kinetic resolution of P‐chiral secondary phosphine oxides. It thus provides an expedient approach to access the enantiomers of the P‐chiral tertiary phosphine oxides derived from asymmetric hydrophosphinylation, further improving the utility of the method.

Catalytic Asymmetric Hydrophosphinylation of 2-Vinylazaarenes to Access P-Chiral 2-Azaaryl-Ethylphosphine Oxides.

A chiral Brønsted acid-catalysed asymmetric hydrophosphinylation of 2-vinylazaarenes by secondary phosphine oxides is described. A variety of P-chiral 2-azaaryl-ethylphosphine oxides are synthesized with high yields and ees, of which both the substituents of phosphines and azaarenes can be flexibly modulated, underscoring an exceptionally broad scope of substrates. These adducts are valuable to asymmetric metal catalysis since the resultant P-chiral tertiary phosphines from the reduction of them are verified as a kind of effective C1 -symmetric chiral 1,5-hybrid P,N-ligands. Importantly, this catalysis platform enables the generic and efficient kinetic resolution of P-chiral secondary phosphine oxides. It thus provides an expedient approach to access the enantiomers of the P-chiral tertiary phosphine oxides derived from asymmetric hydrophosphinylation, further improving the utility of the method.

Preparation of Coupling Catalyst HamZIF-90@Pd@CALB with Tunable Hollow Structure for Efficient Dynamic Kinetic Resolution of 1-Phenylethylamine.

Chiral amines are essential components for many pharmaceuticals and agrochemicals. However, the difficulty in obtaining enantiomerically pure amines limits their application. In this study, hollow amorphous ZIF-90 (HamZIF-90) materials were prepared by template engraving, and chemical-enzyme coupling catalysts (HamZIF-90@Pd@CALB) were constructed for the chiral resolution of 1-phenylethylamine. Different from conventional materials, HamZIF-90 had tunable hollow structures by altering its central node zinc ion concentrations, and the embedded hydrogel template gave it more pore structures, which facilitated the loading of enzyme molecules and Pd nanoparticles (NPs). The establishment of the coupling catalysts shortened the mass transfer distance of the reactant molecules between the metal nanoparticles and the enzyme catalyst in the dynamic kinetic resolution (DKR) reaction, resulting in 98% conversion of 1-phenylethylamine and 93% selectivity of Sel.R-amide. The proposal of this idea provided a good idea for future tailor-made MOFs loaded with chemical and enzyme coupled catalyst.

Anion effect on enantioselective oxidative NHC catalysis: highly efficient kinetic resolution of tertiary alcohols and beyond

The effect of the counter-anion in the azolium pre-catalyst on enantio-control in oxidative NHC catalysis is demonstrated systematically for the first time in acylative kinetic resolution of oxindole-derived tertiary alcohols.

Kinetic resolution of heterobiaryl N-oxides by asymmetric C–H olefination: an expeditious access to (R)-QUINAP

A highly efficient kinetic resolution of heterobiaryl N-oxides through asymmetric C–H olefination was realized to provide two types of 1-arylisoquinoline N-oxides with excellent enantioselectivity (up to 97% ee and 99% ee, respectively).

Open Nitrogen Site-Induced Kinetic Resolution and Catalysis of a Gold Nanocluster.

The emerging metal nanocluster provides a platform for the investigation of structural features, unique properties, and structure-property correlation of nanomaterials at the atomic level. Construction of open sites on the surface of the metal nanocluster is a long-pursued but challenging goal. Herein, we realized the construction of "open organic sites" in a metal nanocluster for the first time. Specifically, we introduce the PNP (2,6-bis(diphenylphosphinomethyl)pyridine) pincer ligand in the synthesis of the gold nanocluster, enabling the construction of a structurally precise Au8(PNP)4 nanocluster. The rigidity and the unique bonding mode of PNP lead to open nitrogen sites on the surface of the Au8(PNP)4 nanocluster, which have been utilized as multifunctional sites in this work for efficient kinetic resolution and catalysis. The gold pincer nanocluster and the open nitrogen site-induced performance will be enlightening for the construction of multifunctional metal nanoclusters.

Asymmetric synthesis of flavanols via Cu-catalyzed kinetic resolution of chromenes and their anti-inflammatory activity.

Flavanols are privileged heterocyclic compounds in medicinal chemistry. It is notable to develop an efficient and straightforward protocol for accessing chiral flavanols with precise control of the stereocenters. Here, a highly efficient kinetic resolution of chromenes was reported via Cu-catalyzed asymmetric hydroboration. This previously unidentified approach features a one-step synthesis of chiral flavan-3-ols containing two vicinal stereogenic centers via a highly efficient kinetic resolution (s factor up to 1060, >99% ee for most products). In addition, the anti-inflammation effects of these diversified flavan-3-ols were studied by the in vitro experiments and RNA sequencing analysis. These flavan-3-ols showed inhibitory effects on the secretion of pro-inflammation cytokines including interleukin-1β (IL-1β), IL-6, and tumor necrosis factor–α (TNF-α), as well as inhibiting the inflammation responses through down-regulating the gene transcriptions closely related to PI3K-Akt signaling pathway and TNF signaling pathway. The results suggested that these newly synthesized flavan-3-ols have the potential to be lead compounds for anti-inflammatory drugs.

Kinetic Resolution of 1,2‐Diaminesvia Organocatalyzed Asymmetric Electrophilic Aminations of Anilines

Comprehensive SummaryAn efficient kinetic resolution (KR) protocol for 1,2‐diamines has been developed through asymmetric electrophilic aminations of anilines enabled by chiral phosphoric acid catalysis. A wide array of substituted 1,2‐diamines were compatible with this method, generating both the recovered staring materials and the amination products with high enantioselectivities (withs‐factor up to 218). Notably, this method is amenable to the kinetic resolution of 1,2‐diamines bearing α‐tertiary amine moieties, which represents the first KR of this type of 1,2‐diamines. Facile removal of the introduced hydrazine group and oxidative cleavage of theN‐aryl group to release the free primary amine demonstrate the value of this method.

Enantiocontrol over Acyclic Quaternary Stereocenters by Acylative Organocatalyzed Kinetic Resolution

AbstractIn the present paper, we described the efficient enantioselective kinetic resolution (KR) of racemic diastereocontrolled secondary alcohols bearing a quaternary stereocenter using a commercially available chiral isothiourea organocatalyst. This methodology is a general KR leading to the enantiocontrol of acyclic quaternary stereocenter with high levels of stereoselectivity (s up to 185) on a large scope. The hydroxyl function can easily serve as a traceless group by oxidation or reduction process.

ArPNO-catalyzed acylative kinetic resolution of tertiary alcohols: access to 3-hydroxy-3-substituted oxindoles.

Bifunctional chiral 4-aryl-pyridine-N-oxides (ArPNO) were reported for the acylative kinetic resolution of 3-hydroxy-3-substituted oxindoles, where the oxygen acts as the nucleophilic site. Using less sterically hindered acetic anhydride, both the recovered tertiary heterocyclic alcohols and the ester products exhibited good to excellent results with s-factors up to 167. Control experiments supported the dual activation manner, where the N-oxide group and N-H proton in ArPNO were crucial for high selectivity and enhanced catalytic reactivity. Compared with the extensively used chiral NHC, isochalcogenourea, and DMAP catalysts, we found that chiral ArPNO were also efficient organocatalysts in the kinetic resolution of tertiary alcohols.

Dynamic kinetic resolution of transient hemiketals: a strategy for the desymmetrisation of prochiral oxetanols.

Identification of an electron poor trifluoroacetophenone allows the formation of uniquely stable hemiketals from prochiral oxetanols. When exposed to a cobalt(ii) catalyst, efficient ring-opening to densely functionalized dioxolanes is observed. Mechanistic studies suggest an unprecedented redox process between the cobalt(ii) catalyst and the hemiketal that initiates the oxetane-opening. Based on this observation, a dynamic kinetic resolution of the transient hemiketals is explored that uses a Katsuki-type ligand for stereoinduction (up to 99 : 1 dr and 96 : 4 er) and allows a variety of 1,3-dioxolanes to be accessed (20 examples up to 98% yield).

Iridium-catalyzed enantioselective alkynylation and kinetic resolution of alkyl allylic alcohols.

Herein, we report an efficient kinetic resolution of alkyl allylic alcohols enabled by an iridium-catalyzed enantioselective alkynylation of alkyl allylic alcohols with potassium alkynyltrifluoroborates. A wide range of chiral 1,4-enynes bearing various functional groups and unreacted enantioenriched allylic alcohols were obtained with excellent enantioselectivities and high kinetic resolution performance (s-factor up to 922). Additionally, this method is particularly effective for preparing some useful optically pure alkyl allylic alcohols, such as the key components towards the synthesis of prostaglandins and naturally occurring matsutakeols, which are difficult to access via other asymmetric reactions. Mechanistic studies revealed that the efficient kinetic resolution might be due to the significant distinction of the η 2-coordination between the (R)- and (S)-allylic alcohols with the iridium/(phosphoramidite, olefin) complex.