Asymmetric Synthesis Research Articles

Stereoselective Synthesis of AB‐5,15‐Porphyrinquinone Platinum(II) Complexes

5,15‐Porphyrinquinone is a non‐aromatic and electron‐deficient porphyrinoid that acts as an important framework for the synthesis of porphyrinoid derivatives. Generally, meso‐functionalized A2‐porphyrinquinone is synthesized via the oxidation of A2‐porphyrin. Herein, we present the stereoselective synthesis of AB‐porphyrinquinone Pt(II) complexes using the corresponding dipyrrinato‐Pt complexes and bisformyldipyrrins. The reaction involves cyclization and oxidative aromatization induced by the Pt template, followed by oxidation using a mild MnO2 oxidant.

Quaternary Chiral Phthalides Enabled by Dirhodium(II)/Phosphine Catalyzed Asymmetric Carbonyl Addition Cascade.

The catalytic asymmetric synthesis of chiral phthalides has garnered considerable interest. However, the construction of phthalides with a chiral quaternary carbon stereocenter still remains challenging. In this study, we developed a new strategy toward catalytic asymmetric synthesis of chiral 3,3-disubstituted phthalides via a dirhodium(II)/phosphine-catalyzed carbonyl addition cascade, yielding phthalides with up to 97% ee values. The reaction proceeded through dirhodium(II)/phosphine-catalyzed asymmetric carbonyl addition of arylboronic acids to isoquinoline-1,3,4(2H)-triones, followed by base-mediated ring contraction.

Direct Asymmetric Synthesis of α-Aminoimines from 1,2-Bis-N-Sulfinylimines by Using Allyl Boronic Acids.

A unique direct asymmetric synthesis of α-aminoimines is realized, through rapid and exclusive mono-allylation of chiral bis-N-sulfinylimines using allylboronic acids. The highly selective allylation was possible as electrophilic imine functional group in the product α-aminoimines remained unreactive towards allyl boronic acid nucleophiles. Notably, by varying the geometry and chiral auxiliary, all four isomers of the α-aminoimines were accessed from readily available precursors. A range of allyl nucleophiles, which are tricky to generate by other means possessing highly reactive functional groups also took part in this reaction, expanding the scope further. The applicability of the products α-aminoimines were further demonstrated by accessing a range of structurally diverse chiral cyclic and acyclic 1,2-diamines bearing adjacent stereocenters through addition of a second nucleophile or aza-Prins-type cyclization by exploiting the nucleophilicity of the tethered alkene moiety. Moreover, the leaving group aptitude of sulfinyl auxiliary attached to imine, was exploited to access valuable chiral α-aminonitriles under thermal conditions without employing any reagents. Detailed DFT calculation revealed a chair-like transition state likely operating for the allylboration reaction across imine.

Direct Asymmetric Synthesis of α‐Aminoimines from 1,2‐Bis‐N‐Sulfinylimines by Using Allyl Boronic Acids

AbstractA unique direct asymmetric synthesis of α‐aminoimines is realized, through rapid and exclusive mono‐allylation of chiral bis‐N‐sulfinylimines using allylboronic acids. The highly selective allylation was possible as electrophilic imine functional group in the product α‐aminoimines remained unreactive towards allyl boronic acid nucleophiles. Notably, by varying the geometry and chiral auxiliary, all four isomers of the α‐aminoimines were accessed from readily available precursors. A range of allyl nucleophiles, which are tricky to generate by other means possessing highly reactive functional groups also took part in this reaction, expanding the scope further. The applicability of the products α‐aminoimines were further demonstrated by accessing a range of structurally diverse chiral cyclic and acyclic 1,2‐diamines bearing adjacent stereocenters through addition of a second nucleophile or Prins‐type cyclization by exploiting the nucleophilicity of the tethered alkene moiety. Moreover, the leaving group aptitude of sulfinyl auxiliary attached to imine, was exploited to access valuable chiral α‐aminonitriles under thermal conditions without employing any reagents. Detailed DFT calculation revealed a chair‐like transition state, arising from corresponding allylboroxine species, likely operating for the allylboration reaction across imine.

Recent Advances on Catalytic Atroposelective Synthesis of Planar‐Chiral Macrocycles

AbstractPlanar‐chiral skeletons widely exist in natural products, bioactive compounds, and other functional molecules. Although significant progress has been made in the field of asymmetric synthesis of centrally or axially chiral molecules over the past years, enantioselective constructing of planar chirality is still a big obstacle and numerous efforts have been made in this field. Previous works have mainly focused on the assembly of planar‐chiral [2,2]‐paracyclophanes and metallocenes. This Minireview describes recent advancements in asymmetric catalytic synthesis of planar‐chiral macrocycles, including ansa chain construction, plane formation and asymmetric transformation strategies. It is anticipated that this Minireview will sever as a source of inspiration for developing new unconventional procedures for access to planar‐chiral skeletons.

Recent Advances on Catalytic Atroposelective Synthesis of Planar-Chiral Macrocycles.

Planar chiral skeletons widely exist in natural products, bioactive compounds, and other functional molecules. Although significant progress has been made in the field of asymmetric synthesis of central or axial chiral molecules over the past years, enantioselective constructing of planar chirality is still a big obstacle and numerous efforts have been made in this field. Previous works have mainly focused on the assembly of planar chiral [2,2]-paracyclophanes and metallocenes. This Minireview describes the recent advancements on asymmetric catalytic synthesis of planar chiral macrocycles, including ansa chain construction, plane formation and asymmetric transformation strategies. It is anticipated that this Minireview will sever as a source of inspiration for developing new unconventional procedures for access to planar chiral skeletons.

Chemodivergent Parallel Kinetic Resolution of Paracyclophanes: Enantiomer Fishing with Different Substrates

AbstractAn unprecedented chemodivergent strategy for parallel kinetic resolution (PKR) is disclosed through which two planar chiral products bearing different structures were simultaneously afforded with opposite stereoselectivities. Two achiral esters are activated by one single chiral N‐heterocyclic carbene (NHC) catalyst to react with the different enantiomers of the racemic imine substrate in a parallel fashion. Two products bearing distinct structures and opposite stereoselectivities are respectively afforded from the same reaction system in good to excellent yields, enantio‐ and diastereoselectivities. Control experiments and kinetic studies are carried out to probe the kinetic and dynamic properties during the reaction progress. The planar chiral pyridine and lactam products show interesting applications in both asymmetric synthesis and pesticide development.

Chemodivergent Parallel Kinetic Resolution of Paracyclophanes: Enantiomer Fishing with Different Substrates.

An unprecedented chemodivergent strategy for parallel kinetic resolution (PKR) is disclosed through which two planar chiral products bearing different structures were simultaneously afforded with opposite stereoselectivities. Two achiral esters are activated by one single chiral N-heterocyclic carbene (NHC) catalyst to react with the different enantiomers of the racemic imine substrate in a parallel fashion. Two products bearing distinct structures and opposite stereoselectivities are respectively afforded from the same reaction system in good to excellent yields, enantio- and diastereoselectivities. Control experiments and kinetic studies are carried out to probe the kinetic and dynamic properties during the reaction progress. The planar chiral pyridine and lactam products show interesting applications in both asymmetric synthesis and pesticide development.

4+2] Cycloaddition Mediated Stereoselective Synthesis of Tetrahydro‐1H‐Isobenzofuro Chromene Dione Derivatives: Antibacterial Evaluation and Molecular Docking Investigation

AbstractAn efficient stereoselective synthesis of tetrahydro‐1H‐isobenzofuro[4,5‐c]chromene‐1,3(3aH)‐dione derivatives were achieved through a novel [4+2] cycloaddition reaction of 4‐styryl‐2H‐chromenes with cheaply available maleic anhydride. A series of new tetrahydro‐1H‐isobenzofuro[4,5‐c]chromene‐1,3(3aH)‐dione derivatives 21(a–p) were synthesized in good to excellent yield under mild reaction condition with no chromatographic purification. In this reaction, the generation of four new consecutive stereogenic centers were determined by single crystal X‐ray analysis. All the synthesized compounds were investigated further in silico and in vitro for antibacterial activities using two bacterial strain of DNA gyrase. Compounds 21 b and 21 j showed excellent docking score −9.3 kCal/mol and −8.6 kCal/mol with gram negative bacterial strain Escherichia coli (E. coli) with protein data bank (PDB ID) 3G7E. Out of all the tested molecules, 21 b and 21 j displayed good results with minimum inhibitory concentration 10 μg/ml, 10 μg/ml against the bacterial strain Escherichia coli(E. coli) and 10 μg/ml, 20 μg/ml against Staphylococcus aureus (S. aureus) respectively.

TMSOTf Mediated Aminocyclization/[1,3]‐Sulfonyl Migration on N‐Homopropargyl Hydroxylamines for the Stereoselective Synthesis of 3‐Sulfonyl Cyclic Nitrones

TMSOTf‐mediated 5‐endo‐dig aminocyclization followed by N‐ to C‐[1,3]‐sulfonyl migration on N¬‐homopropargyl hydroxylamines gave diastereoselective access to trisubstituted 3‐sulfonyl cyclic nitrone (3‐sulfonyl pyrroline N‐oxide) derivatives. The synthetic utility of the 3‐sulfonyl cyclic nitrone products was demonstrated through the diastereoselective synthesis of the sulfonyl‐substituted nonaromatic N‐heterocycles such as N‐hydroxy pyrrolidine, pyrrolidine‐fused isoxazoline, and isoxazolidine derivatives.

Asymmetric Synthesis of Chiral Cyclopropanes from Vinyl Sulfoxonium Ylides Catalyzed by a Chiral-at-Metal Rh(III) Complex.

A chiral-at-metal Rh(III) complex-mediated [2+1] cyclization of vinyl sulfoxonium ylides with α,β-unsaturated 2,2-acylimidazoles has been demonstrated for the first time. This work provides a practical approach for assembling 1,2,3-trisubstituted chiral cyclopropane with alkyl structural units, which had advantages such as a wide range of substrates, good functional group tolerance, and mild reaction conditions. In addition, further amplification experiments and transformation of cycloaddition products were carried out to highlight the practicality of the method.

Visible-light-driven asymmetric aldol reaction of ketones and glycinates via synergistic Lewis acid/photoredox catalysis.

Visible-light-driven direct asymmetric α-C(sp3)-H bond functionalization of glycinate provides a direct and efficient route for the synthesis of diverse optically enriched α-amino acid derivatives. However, asymmetric coupling between glycinate radical species and ketones faces significant challenges, including competitive pathways, mutable intermediates, as well as congested stereogenic centers. Herein, we disclose the first example for the asymmetric photocatalytic synthesis of a diverse array of β-diaryl-β-hydroxy-α-amino acetate derivatives from glycinates and heteroaryl ketones through the synergistic catalysis of achiral iridium photoredox catalyst and chiral lanthanide Lewis acid catalysts. The enantioselective radical addition pathway is supported by spectroscopic experiments, control experiments and DFT calculations.

Asymmetric organocatalytic synthesis of chiral homoallylic amines.

In recent decades, the chiral allylation of imines emerged as a key methodology in the synthesis of alkaloids and natural products with 4-, 5- and 6-membered cyclic amine motifs. Initially reliant on stoichiometric reagents, synthetic chemists predominantly used N-substituted chiral imines, organometallic chiral reagents and achiral reagents with an equimolar chiral controller. However, recent years have witnessed the rise of asymmetric transition-metal catalysts and, importantly, organocatalytic allylation, reshaping the landscape of modern synthetic chemistry. This review explores the latest developments in the asymmetric allylation of imines, encompassing cutting-edge advances in hydrogen-bond catalysis and non-classical approaches. Furthermore, practical examples showcasing the application of these innovative methodologies in total synthesis are presented.

Spin Dynamics of Radical Pairs Using the Stochastic Schrödinger Equation in MolSpin.

The chemical reactivity of radical pairs is strongly influenced by the interactions of electronic and nuclear spins. A detailed understanding of these effects requires a quantum description of the spin dynamics that considers spin-dependent reaction rates, interactions with external magnetic fields, spin-spin interactions, and the loss of spin coherence caused by coupling to a fluctuating environment. Modeling real chemical and biochemical systems, which frequently involve radicals with multinuclear spin systems, poses a severe computational challenge. Here, we implement a method based on the stochastic Schrödinger equation in the software package MolSpin. Large electron-nuclear spin systems can be simulated efficiently, with asymmetric spin-selective recombination reactions, anisotropic hyperfine interactions, and nonzero exchange and dipolar couplings. Spin-relaxation can be modeled using the stochastic time-dependence of spin interactions determined by molecular dynamics and quantum chemical calculations or by allowing rate coefficients to be explicitly time-dependent. The flexibility afforded by this approach opens new avenues for exploring the effects of complex molecular motions on the spin dynamics of chemical transformations.

Improvement of bifunctional organocatalysts performance by water as an additive in the Michael addition of carbonyl compounds to maleimides

The diastereoselective Michael addition of ketones to maleimides using bifunctional organocatalysts presents a significat challenge. We developed a protocol in which the addition of 5 equivalents of water boosted the diastereoselectivity of six-membered ring ketones. However, the results were influenced by steric effects and varied outcomes were observed with different ring sizes of ketones and acyclic carbonyl compounds. The improvement in the asymmetric synthesis of succinimides due to water appears to be more related to hydrogen bonds at the interface rather than a water molecule embedded in the transition state. Additionally, we explored 3-substituted maleimides and found that only those with phenyl and phenylethynyl groups underwent the reaction. Finally, the desymmetrization of N-(2-tert-butylphenyl)maleimide generated the atropoisomer with good selectivity.

Enantiopure P-Chiral Secondary Phosphines (P*HRR') from the Catalytic Asymmetric Hydrogenation of P═C Bonds.

We report the first bottleable enantiopure P-chiral secondary phosphines from the rhodium-catalyzed asymmetric hydrogenation of phosphaalkenes. Catalytic asymmetric hydrogenation, a reaction of broad academic and industrial importance for C═C, N═C, and O═C bonds, has not previously been reported for the P═C bond. The hydrogenation of ArP═CR2 (Ar = Mes, m-Xyl and TMOP; R = Ph, 4-C6H4F) affords four unprecedented P-stereogenic secondary phosphines in 76%-90% isolated yields with 91%-97% enantiomeric excess (ee). These isolable P-chiral secondary phosphines are configurationally stable indefinitely in the solid state and show only modest loss in ee when kept in solution for over a month at room temperature.

Stereoselective and site-divergent synthesis of C-glycosides.

Carbohydrates play important roles in medicinal chemistry and biochemistry. However, their synthesis relies on specially designed glycosyl donors, which are often unstable and require multi-step synthesis. Furthermore, the catalytic and stereoselective installation of arylated quaternary stereocentres on sugar rings remains a formidable challenge. Here we report a facile and versatile method for the synthesis of diverse C-R (where R is an aryl, heteroaryl, alkenyl, alkynyl or alkyl) glycosides from readily available and bench-stable 1-deoxyglycosides. The reaction proceeds under mild conditions and exhibits high stereoselectivity across a broad range of glycosyl units. This protocol can be used to synthesize challenging 2-deoxyglycosides, unprotected glycosides, non-classical glycosides and deuterated glycosides. We further developed the catalyst-controlled site-divergent functionalization of carbohydrates for the synthesis of various unexplored carbohydrates containing arylated quaternary stereocentres that are inaccessible by existing methods. The synthetic utility of this strategy is further demonstrated in the synthesis of pharmaceutically relevant molecules and carbohydrates.

Mass transfer-enhanced platform for heterogeneous dual organocatalysis to boost yield and diastereoselectivity in enantioselective Michael/benzoin cascade reaction

Mass transfer limitation and tedious anchoring of multiple expensive chiral organocatalysts are the key bottlenecks in heterogeneous asymmetric cascade/tandem reactions, leading to high-cost processes with low catalytic performances. In this paper, two chiral organocatalysts, including (S)-diphenylprolinoltrimethylsilyl ether (ProTMS) and N-heterocyclic carbenes (NHC), are simultaneously immobilized to hollow mesoporous polystyrene nanospheres (HMPNs) in one-pot via Friedel-Crafts alkylation to afford supported dual organocatalysts (ProTMS&NHC@HMPNs) at low cost. The catalyst possesses the spherical morphology with a hollow interior and a thin mesopore-abundant shell, providing suitable environments for reactants to quickly access to the catalytic sites of NHC and ProTMS. The side reactions caused by limited mass transfer are effectively suppressed, and superior yields (70–92 %) and diastereoselectivities (dr = 3:120:1) to homogeneous catalysis are achieved in heterogeneous Michael/benzoin cascade reaction. Overall, the mass transfer-enhanced platform for efficient heterogeneous dual organocatalysis is developed to boost yield and diastereoselectivity in asymmetric cascade reactions.

De Novo Enantioselective Synthesis of Hexafluorinated d-Glucose.

We report a de novo enantioselective synthesis of 2,3,4-trideoxy-2,2,3,3,4,4-hexafluoro-d-glycero-hexopyranose (hexafluorinated d-glucose), an iconic polar hydrophobic glycomimetic. The 12-step synthesis features robust and reproducible chemistry and was achieved by incorporating an asymmetric dihydroxylation step to install the stereogenic center with excellent enantioselectivity (95:5 er). Virtual enantiopurity (>99.5% ee) was further reached using a simple crystallization procedure and the absolute confirmation was ascertained by X-ray analysis. The synthetic route also allowed access to the novel hexafluorinated heptose derivative 2,3,4-trideoxy-2,2,3,3,4,4-hexafluoro-l-threo-heptopyranose.

Enantioselective S‐Alkylation of Sulfenamides by Phase‐Transfer Catalysis

AbstractA general phase‐transfer catalyst (PTC) mediated enantioselective alkylation of N‐acylsulfenamides is reported. Essential to achieving high selectivity was the use of the triethylacetyl sulfenamide protecting group along with aqueous KOH as the base under biphasic aqueous conditions to enable the reaction to be performed at −40 °C. With these key parameters, enantiomeric ratios up to 97.5 : 2.5 at the newly generated chiral sulfur center were achieved with an inexpensive cinchona alkaloid derived PTC. Broad scope and excellent functional group compatibility was observed for a variety of S‐(hetero)aryl and branched and unbranched S‐alkyl sulfenamides. Moreover, to achieve high selectivity for the opposite enantiomer, a pseudoenantiomeric catalyst was designed and synthesized from inexpensive cinchonidine. Given that sulfoximines are a bioactive pharmacophore of ever‐increasing interest, selected product sulfilimines were oxidized to the corresponding sulfoximines with subsequent reductive cleavage affording the free‐NH sulfoximines in high yields. The utility of the disclosed method was further demonstrated by the efficient asymmetric synthesis of atuveciclib, a phase I clinical candidate for which only chiral HPLC separation had previously been reported for isolation of the desired (R)‐sulfoximine stereoisomer.