Catalytic Asymmetric Construction of Quaternary α‐Amino Acid Containing Pyrrolidines through 1,3‐Dipolar Cycloaddition of Azomethine Ylides to α‐Aminoacrylates

The first catalytic enantioselective 1,3‐dipolar cycloaddition of azomethine ylides to α‐aminoacrylate catalyzed by a AgOAc/ferrocenyl oxazolinylphosphine (FOXAP) system was developed, which exhibits excellent exo‐ and enantioselectivity (92–99 % ee). This process provides efficient access to useful 4‐aminopyrrolidine‐2,4‐dicarboxylic acid (APDC)‐like compounds containing a unique quaternary α‐amino acid unit.     

Enantioselective Synthesis of Chiral Isotopomers of 1‐Alkanols by a ZACA–Cu‐Catalyzed Cross‐Coupling Protocol

Chiral compounds arising from the replacement of hydrogen atoms by deuterium are very important in organic chemistry and biochemistry. Some of these chiral compounds have a non‐measurable specific rotation, owing to very small differences between the isotopomeric groups, and exhibit cryptochirality. This particular class of compounds is difficult to synthesize and characterize. Herein, we present a catalytic and highly enantioselective conversion of terminal alkenes to various β and more remote chiral isotopomers of 1‐alkanols, with ≥99 % enantiomeric excess (ee), by the Zr‐catalyzed asymmetric carboalumination of alkenes (ZACA) and Cu‐catalyzed cross‐coupling reactions. ZACA‐in situ iodinolysis of allyl alcohol and ZACA‐in situ oxidation of TBS‐protected ω‐alkene‐1‐ols protocols were applied to the synthesis of both (R)‐ and (S)‐difunctional intermediates with 80–90 % ee. These intermediates were readily purified to provide enantiomerically pure (≥99 % ee) compounds by lipase‐catalyzed acetylation. These functionally rich intermediates serve as very useful synthons for the construction of various chiral isotopomers of 1‐alkanols in excellent enantiomeric purity (≥99 % ee) by introducing deuterium‐labeled groups by Cu‐catalyzed cross‐coupling reactions without epimerization.     

Facile Synthesis of Chiral Cyclic Ureas through Hydrogenation of 2‐Hydroxypyrimidine/Pyrimidin‐2(1H)‐one Tautomers

A facile access to optically active cyclic ureas was developed through palladium‐catalyzed asymmetric hydrogenation of pyrimidines containing tautomeric hydroxy group with up to 99 % ee. Mechanistic studies indicated that reaction pathway proceed through hydrogenation of C=N of the oxo tautomer pyrimidin‐2(1H)‐one, acid‐catalyzed isomerization of enamine–imine, and hydrogenation of imine pathway. In addition, the chiral cyclic ureas are readily converted into useful chiral 1,3‐diamine and thiourea derivatives without loss of optical purity.     

Enantioselective Cascade Michael Addition/Cyclization Reactions of 3‐Nitro‐2H‐Chromenes with 3‐Isothiocyanato Oxindoles: Efficient Synthesis of Functionalized Polycyclic Spirooxindoles

An unprecedented Zn(OTf)₂‐catalyzed asymmetric Michael addition/cyclization cascade of 3‐nitro‐2H‐chromenes with 3‐isothiocyanato oxindoles has been disclosed. This transformation provides an efficient access to various synthetically important polycyclic spirooxindoles in a highly stereoselective manner under mild conditions (72–99 % yields, up to >95:5 d.r. and >99 % ee). The reaction leads to the formation of three consecutive stereocenters, including 1,3‐nonadjacent tetrasubstituted carbon stereocenters, in a single operation. A bifunctional activation model of the chiral Zn(OTf)₂/bis(oxazoline) complex was proposed based on control experiments, wherein the Zn^II moiety serves as a Lewis acid and the N atom of the free NH group acts as a Lewis base by a hydrogen‐bonding interaction.     

Octahedral Chiral‐at‐Metal Iridium Catalysts: Versatile Chiral Lewis Acids for Asymmetric Conjugate Additions

Octahedral iridium(III) complexes containing two bidentate cyclometalating 5‐tert‐butyl‐2‐phenylbenzoxazole ( IrO ) or 5‐tert‐butyl‐2‐phenylbenzothiazole ( IrS ) ligands in addition to two labile acetonitrile ligands are demonstrated to constitute a highly versatile class of asymmetric Lewis acid catalysts. These complexes feature the metal center as the exclusive source of chirality and serve as effective asymmetric catalysts (0.5–5.0 mol % catalyst loading) for a variety of reactions with α,β‐unsaturated carbonyl compounds, namely Friedel–Crafts alkylations (94–99 % ee), Michael additions with CH‐acidic compounds (81–97 % ee), and a variety of cycloadditions (92–99 % ee with high d.r.). Mechanistic investigations and crystal structures of an iridium‐coordinated substrates and iridium‐coordinated products are consistent with a mechanistic picture in which the α,β‐unsaturated carbonyl compounds are activated by two‐point binding (bidentate coordination) to the chiral Lewis acid.     

Highly Enantioselective Synthesis of α‐Stereogenic Esters through Catalytic Asymmetric Michael Addition of 4‐Oxo‐4‐arylbutenoates

Highly enantioselective Michael addition of 1,3‐dicarbonyl compounds and nitromethane to 4‐oxo‐4‐arylbutenoates catalyzed by N,N′‐dioxide–Sc(OTf)₃ complexes has been developed. Using 0.5–2 mol % catalyst loading, various α‐stereogenic esters were obtained regioselectively with excellent yields (up to 97 %) and enantioselectivities (up to >99 % ee). Moreover, the reaction performed well under nearly solvent‐free conditions. The products with functional groups are ready for further transformation, which showed the potential value of the catalytic approach. According to the experimental results and previous reports, a plausible working model has been proposed to explain the origin of the activation and the asymmetric induction.     

Gold(I)/Chiral N,N′-Dioxide–Nickel(II) Relay Catalysis for Asymmetric Tandem Intermolecular Hydroalkoxylation/Claisen Rearrangement

A highly efficient asymmetric cascade reaction between alkynyl esters and allylic alcohols has been realized. Key to success was the combination of a hydroalkoxylation reaction catalyzed by a π-acidic gold(I) complex with a Claisen rearrangement catalyzed by a chiral Lewis acidic N,N′-dioxide–nickel(II) complex. A range of acyclic α-allyl β-keto esters were synthesized in high yields (up to 99 %) with good diastereoselectivities (up to 97:3) and excellent enantioselectivities (up to 99 % ee) under mild reaction conditions. These products can be easily transformed into optically active β-hydroxy esters, β-hydroxy acids, or 1,3-diols.     

Construction of Optically Active Quaternary Propargyl Amines by Highly Enantioselective Zinc/BINOL‐Catalyzed Alkynylation of Ketoimines

A general and efficient method for the highly enantioselective alkynylation of ketoimines through a zinc/1,1′‐bi‐2‐naphthol (BINOL)‐catalyzed process has been developed. A variety of ketoimines, including α‐fluoroalkyl α‐imine esters, α‐aryl α‐imine esters, and trifluoromethyl aryl ketoimines, are applicable and provide their corresponding quaternary propargyl amines in excellent yields with high ee values (up to 99 % ee). Both the steric and electronic effects of substituents at the 3,3′ positions of BINOL are critical for the reaction efficiency and enantioselectivity. To demonstrate the usefulness of the method, (R)‐α‐CF₃ α‐proline has been prepared in a highly efficient manner. The notable features of this protocol are its broad substrate scope, high reaction efficiency (up to 99 %) and enantioselectivity (up to 99 % ee), low catalyst loading (5 mol % of BINOL derivative), and mild reaction conditions.     

CuII‐Containing 1‐Aminocyclopropane Carboxylic Acid Oxidase Is an Efficient Stereospecific Diels–Alderase

In the context of developing ecofriendly chemistry, artificial enzymes are now considered as promising tools for synthesis. They are prepared in particular with the aim to catalyze reactions that are rarely, if ever, catalyzed by natural enzymes. We discovered that 1‐aminocyclopropane carboxylic acid oxidase reconstituted with Cu^II served as an efficient artificial Diels–Alderase. The kinetic parameters of the catalysis of the cycloaddition of cyclopentadiene and 2‐azachalcone were determined (K_M=230 μm , k_app=3 h^?1), which gave access to reaction conditions that provided quantitative yield and >99 % ee of the (1S,2R,3R,4R) product isomer. This unprecedented performance was rationalized by molecular modeling as only one docking pose of 2‐azachalcone was possible in the active site of the enzyme and this was the one that leads to the (1S,2R,3R,4R) product isomer.     

Asymmetric Hydrocyanation of Alkenes without HCN

A general and efficient rhodium‐catalyzed asymmetric cyanide‐free hydrocyanation of alkenes has been developed. Based on the asymmetric hydroformylation/condensation/aza‐Cope elimination sequences, a broad scope of substrates including mono‐substituted, 1,2‐, and 1,1‐disubstituted alkenes (involving natural product R‐ and S‐limonene) were employed, and a series of valuable chiral nitriles are prepared with high yields (up to 95 %) and enantioselectivities (up to 98 % ee). Notably, the critical factor to achieve high enantioseletivies is the addition of catalytic amount of benzoic acid. This novel methodology provides an efficient and concise synthetic route to the intermediate of vildagliptin and anagliptin.     

Enantiopure Narrow Bite‐Angle POP Ligands: Synthesis and Catalytic Performance in Asymmetric Hydroformylations and Hydrogenations

Herein is reported the preparation of a set of narrow bite‐angle P–OP ligands the backbone of which contains a stereogenic carbon atom. The synthesis was based on a Corey–Bakshi–Shibata (CBS)‐catalyzed asymmetric reduction of phosphomides. The structure of the resulting 1,1‐P–OP ligands, which was selectively tuned through adequate combination of the configuration of the stereogenic carbon atom, its substituent, and the phosphite fragment, proved crucial for providing a rigid environment around the metal center, as evidenced by X‐ray crystallography. These new ligands enabled very good catalytic properties in the Rh‐mediated enantioselective hydrogenation and hydroformylation of challenging and model substrates (up to 99 % ee). Whereas for asymmetric hydrogenation the optimal P–OP ligand depended on the substrate, for hydroformylation, a single ligand was the highest‐performing one for almost all studied substrates: it contains an R‐configured stereogenic carbon atom between the two phosphorus ligating groups, and an S‐configured 3,3′‐diphenyl‐substituted biaryl unit.     

Enantioselective and Regioselective Organocatalytic Conjugate Addition of Malonates to Nitroenynes

The first catalytic asymmetric conjugate addition of 1,3‐dicarbonyl compounds to nitroenynes catalyzed by cinchona alkaloid‐based thiourea organocatalysts has been developed. The 1,4‐addition adducts were obtained solely, in moderate to good yields (up to 93 %) with good enantioselectivities (up to 99 % ee). This protocol affords a conceptually different entry to the precursors of pharmaceutically important chiral β‐alkynyl acid derivatives and synthetically useful chiral nitroalkynes. Notably, the protocol worked well with both aryl‐ and alkyl‐substituted alkynyl substrates.     

Facile Synthesis of Enantiopure Sugar Alcohols: Asymmetric Hydrogenation and Dynamic Kinetic Resolution Combined

An unprecedented Ir/f‐amphox‐catalyzed asymmetric hydrogenation of racemic 2,3‐syn‐dihydroxy‐1,4‐diones is presented involving dynamic kinetic resolution, which produces (1R,2R,3R,4R)‐tetraols. This protocol constitutes an efficient and straightforward approach to accessing sugar alcohols bearing four contiguous stereocenters. The strategy exhibits various advantages over existing methods, including excellent yields (up to 98 %), exceptional stereoselectivities (up to 99:1 dr, 99.9 % ee), operational simplicity and substrate generality. Moreover, the nature of the reaction was revealed as a stepwise transformation by in situ Fourier‐transform infrared spectroscopy and isolation of intermediates.     

Asymmetric Alkynylation/Lactamization Cascade: An Expeditious Entry to Enantiomerically Enriched Isoindolinones

An unprecedented Cu^I–pybox‐diPh‐catalyzed highly enantioselective (up to >99 % ee) alkynylation/lactamization cascade has been developed as a general catalytic system for the synthesis of diversely substituted isoindolinones of immense biological importance. The cascade effects one C? C and two C? N bond‐forming events in one reaction vessel under operationally simple, additive‐free reaction conditions in good to excellent yields. The methodology was further extended to the synthesis of tetrahydroisoquinoline scaffolds common to several biologically active natural products in a two‐step sequence with remarkable selectivity (up to 94 % ee).     

Chiral N,N′‐Dioxide–Scandium(III) Complex‐Catalyzed Asymmetric Friedel–Crafts Alkylation Reaction of ortho‐Hydroxybenzyl Alcohols with C3‐Substituted N‐Protected Indoles

The first Lewis acid catalyzed asymmetric Friedel–Crafts alkylation reaction of ortho‐hydroxybenzyl alcohols with C3‐substituted indoles is described. A chiral N,N′‐dioxide Sc(OTf)₃ complex served not only to promote formation of ortho‐quinone methides (o‐QMs) in situ but also induced the asymmetry of the reaction. This methodology enables a novel activation of ortho‐hydroxybenzyl alcohols, thus affording the desired chiral diarylindol‐2‐ylmethanes in up to 99 % yield and 99 % ee. A range of functional groups were also tolerated under the mild reaction conditions. Moreover, this strategy gives concise access to enantioenriched indole‐fused benzoxocines.     

Diversified Cycloisomerization/Diels–Alder Reactions of 1,6‐Enynes through Bimetallic Relay Asymmetric Catalysis

We report the combination of transition‐metal‐catalyzed diversified cycloisomerization of 1,6‐enynes with chiral Lewis acid promoted asymmetric Diels–Alder reaction to realize asymmetric cycloisomerization/Diels–Alder relay reactions of 1,6‐enynes with electron‐deficient alkenes. A broad spectrum of chiral [5,6]‐bicyclic products could be acquired in high yields (up to 99 %) with excellent diastereoselectivy (>19:1 dr) and enantioselectivity (up to 99 % ee).     

Practical Enzymatic Desymmetrization of 2‐(Ethoxycarbonyl)propane‐1,3‐diyl Dihexanoate and Model Cyclization for the A–D Ring System of Lysergic Acid

Porcine pancreas lipase‐catalyzed hydrolysis of symmetrical 2‐(ethoxycarbonyl)propane‐1,3‐diyl dihexanoate, under the modified conditions of the Seebach protocol, afforded a desymmetrized monohexanoate in 40–51% yield with 91–94% ee, even in a gram‐scale reaction. The absolute configuration of a half‐hydrolyzed (?)‐product was determined to be (R) by conversion to a known 2‐methylpropane‐1,3‐diol derivative. Samarium iodide‐induced radical cyclization of 2‐oxo‐3‐phenylethylamine with a C₄ unit on the N‐atom, derived from the racemic monohexanoate, afforded a 3‐phenylpiperidine derivative as a model construction of the A–D ring system of lysergic acid.     

Majority‐Rules‐Type Helical Poly(quinoxaline‐2,3‐diyl)s as Highly Efficient Chirality‐Amplification Systems for Asymmetric Catalysis

A highly efficient majority‐rules effect of poly(quinoxaline‐2,3‐diyl)s (PQXs) bearing 2‐butoxymethyl chiral side chains at the 6‐ and 7‐positions was established and attributed to large ΔG_h values (0.22–0.41 kJ mol^?1), which are defined as the energy difference between P‐ and M‐helical conformations per chiral unit. A PQX copolymer prepared from a monomer derived from (R)‐2‐octanol (23 % ee) and a monomer bearing a PPh₂ group adopted a single‐handed helical structure (>99 %) and could be used as a highly enantioselective chiral ligand in palladium‐catalyzed asymmetric reactions (products formed with up to 94 % ee), in which the enantioselectivity could be switched by solvent‐dependent inversion of the helical PQX backbone.     

Desymmetrization of 1,4‐Pentadien‐3‐ol by the Asymmetric 1,3‐Dipolar Cycloaddition of Azomethine Imines

Desymmetrization of the divinyl carbinol 1,4‐pentadien‐3‐ol was accomplished by the asymmetric 1,3‐dipolar cycloaddition of azomethine imines based on a magnesium‐mediated, multinucleating chiral reaction system utilizing diisopropyl (R,R)‐tartrate as the chiral auxiliary. The corresponding optically active trans‐pyrazolidines, each with three contiguous stereogenic centers, were obtained with excellent regio‐, diastereo‐, and enantioselectivity, with results as high as 99 % ee. This reaction was shown to be applicable to both aryl‐ and alkyl‐substituted azomethine imines. The use of a catalytic amount of diisopropyl (R,R)‐tartrate was also effective when accompanied by the addition of MgBr₂.     

Direct Catalytic Asymmetric Mannich Reaction with Dithiomalonates as Excellent Mannich Donors: Organocatalytic Synthesis of (R)‐Sitagliptin

In this study, dithiomalonates (DTMs) were demonstrated to be exceptionally efficient Mannich donors in terms of reactivity and stereoselectivity in cinchona‐based‐squaramide‐catalyzed enantioselective Mannich reactions of diverse imines or α‐amidosulfones as imine surrogates. Owing to the superior reactivity of DTMs as compared to conventional malonates, the catalyst loading could be reduced to 0.1 mol % without the erosion of enantioselectivity (up to 99 % ee). Furthermore, by the use of a DTM, even some highly challenging primary alkyl α‐amidosulfones were smoothly converted into the desired adducts with excellent enantioselectivity (up to 97 % ee), whereas the use of a malonate or monothiomalonate resulted in no reaction under identical conditions. The synthetic utility of the chiral Mannich adducts obtained from primary alkyl substrates was highlighted by the organocatalytic, coupling‐reagent‐free synthesis of the antidiabetic drug (?)‐(R)‐sitagliptin.