Good Ee Research Articles

N-Heterocyclic Carbene-Catalyzed Synthesis of α-Trifluoromethyl Esters

The N-heterocyclic carbene (NHC)-catalyzed trifluoromethylation of α-chloro aldehydes was developed, allowing straightforward access to valuable α-trifluoromethyl ester derivatives. The unique combination of an electrophilic trifluoromethylation reagent with NHC catalysis was the key for the functionalization of a broad range of α-chloro aldehydes, and the products are formed in moderate to good yields. Investigations of the enantioselective version of this reaction afforded the enantioenriched products in moderate yields with good ee values.

Palladium‐Catalyzed Enantioselective Arylation of Racemic Ketones to Form Bridged Bicycles via Dynamic Kinetic Resolution

AbstractEnantioselective α‐arylation of racemic ketones containing existing α′‐stereocenters is reported for the first time via base‐induced dynamic kinetic resolution. Bridged bicyclic rings are formed in good ee values, which are difficult to obtain otherwise. Furthermore, reactions in DMSO‐d6 resulted in extensive deuteration of both α‐ and α′‐positions in the products, thus supporting a pathway involving rapid, reversible deprotonation of ketones under catalytic conditions.

Palladium-Catalyzed Enantioselective Arylation of Racemic Ketones to Form Bridged Bicycles via Dynamic Kinetic Resolution.

Enantioselective α-arylation of racemic ketones containing existing α'-stereocenters is reported for the first time via base-induced dynamic kinetic resolution. Bridged bicyclic rings are formed in good ee values, which are difficult to obtain otherwise. Furthermore, reactions in DMSO-d6 resulted in extensive deuteration of both α- and α'-positions in the products, thus supporting a pathway involving rapid, reversible deprotonation of ketones under catalytic conditions.

Chiral N,N′‐Dioxide/ScΙΙΙ Complex‐Catalyzed Asymmetric Ring‐Opening Reaction of Cyclopropyl Ketones with Indoles

AbstractThe asymmetric ring‐opening reaction of cyclopropyl ketones with indoles has been realized by using a N,N′‐dioxide/scandium(ΙΙΙ) complex as catalyst. The corresponding 3‐alkylated indole derivatives were obtained in moderate to excellent yields with good ee values. Moreover, a possible transition state was proposed on the basis of experimental studies and X‐ray structure of product.magnified image

Cascade Reaction by Chemo- and Biocatalytic Approaches to Obtain Chiral Hydroxy Ketones and anti 1,3-Diols.

A chemo‐ and biocatalytic cascade approach was applied for the stereoselective synthesis of hydroxy ketones and the corresponding 1,3‐diols. A new class of tridentate N,N,O ligands was used with copper(II) complexes for the asymmetric β‐borylation of α,β‐unsaturated compounds. The complex containing ligand L5 emerged as the best performer, and it gave the organoborane derivatives with good ee values. The corresponding keto–alcohol compounds were then bioreduced by yeasts. The biotransformation set up with Rhodotorula rubra allowed (R)‐keto–alcohols and (S,S)‐diols to be obtained with up to 99 % ee and up to 99 % de in favor of the anti enantiomers.

Diastereo- and enantioselective conjugate addition of 3-substituted oxindoles to enones via bifunctional catalysts

This paper presents a synthetically challenging vicinal quaternary-tertiary C–C forming reaction of 3-substituted oxindoles and chalcones by a simple aryl substituted bifunctional thiourea catalyst. The reactions work with a broad range of chalcones, giving chiral 3,3′-substituted oxindoles type compounds with adjacent quaternary-tertiary stereocenters in high yields (up to 99%), very good dr (up to >98:2) and very good ee (up to 96%).

Proteins as Macromolecular Ligands for Metal‐Catalysed Asymmetric Transfer Hydrogenation of Ketones in Aqueous Medium

Biohybrid catalysts resulting from the dative anchoring of half‐sandwich organometallic complexes [M(arene)(H2O)x(Cl)y]n+ (M = RuII, arene = η6‐benzene, p‐cymene or mesitylene; M = IrIII, RhIII, arene = η5‐Cp*; x = 1–3, y = 0–2, n = 0–2) to bovine beta‐lactoglobulin (βLG) or hen egg white lysozyme showed unprecedented behaviour. These constructs were shown to catalyse the asymmetric transfer hydrogenation of aryl ketones in water with sodium formate as hydrogen donor at a much faster rate than the complexes alone. Full conversion of the benchmark substrate 2,2,2‐trifluoroacetophenone was reached with an ee of 86 % for the most selective biohybrid. Surprisingly, even the crude biohybrid gave a good ee despite the presence of non‐protein‐bound metal species in the reaction medium. Other aryl ketones were reduced in the same way, and the highest ee was obtained for ortho‐substituted acetophenone derivatives. Furthermore, treatment of βLG with dimethyl pyrocarbonate resulted in a noticeable decrease of the activity and selectivity of the biohybrid, indicating that the sole accessible histidine residue (His146) was probably involved in the coordination and activation of Ru(benzene). This work underscores that protein scaffolds are efficient chiral ligands for asymmetric catalysis. The use of sodium formate instead of dihydrogen makes this approach safe, inexpensive and environmentally friendly.

Copper-Catalyzed Asymmetric Synthesis of Borylated cis-Disubstituted Indolines.

A copper-catalyzed, intramolecular borylative cyclization of vinyl arenes with imines is reported, which affords enantio-enriched indolines as a single diastereomer under mild conditions. A benzylcopper species is generated by Cu-Bpin addition to the alkene, which then acts as a nucleophile for intramolecular imine addition. The reaction is applicable to various vinyl arenes with an imine moiety at the ortho-position, including heterocycles, for formation of borylated indolines in good yields and ee values up to 90 %.

Iridium-catalyzed asymmetric hydrogenation of 2-substituted 1,4-benzodioxines

An Ir-catalyzed asymmetric hydrogenation of 2-substituted 1,4-benzodioxines was developed for the preparation of chiral 1,4-benzodioxanes, which are present in numerous biologically active compounds and natural products. Our tropos biphenyl phosphine-oxazoline ligand is essential for obtaining good ee. A broad range of substrates were tolerable to the reaction conditions and gave the corresponding hydrogenation products in excellent yields and with moderate to good enantioselectivities using the Ir-complex of our tropos phosphine-oxazoline ligand.

Modular Synthesis of Triazole‐Based Chiral Iodoarenes for Enantioselective Spirocyclizations

AbstractA new triazole‐based C1‐symmetrical chiral iodoarene was synthesized in a highly modular route. Based on enzymatic kinetic resolution of an easily accessible propargylic alcohol both enantiomers were accessible in enantiopure form. By Huisgen‐type azide‐alkyne cycloaddtion a series of differently substituted iodoarenes was synthesized in high overall yields. Finally this novel iodoarene was successfully applied in the oxidative Kita cyclization of naphthol derivatives. Good yields and high ee values were obtained in the asymmetric spirocyclization via in situ generation of the hypervalent iodine species using mCPBA as the terminal oxidant.magnified image

Rhodium(II)/Chiral Phosphoric Acid‐Cocatalyzed Enantioselective O–H Bond Insertion of α‐Diazo Esters

AbstractA rhodium(II)/chiral phosphoric acid system has been developed for the asymmetric catalytic insertion of α‐diazo esters into the O–H bond of carboxylic acids to generate an array of synthetically useful α‐hydroxy ester derivatives in good ee (up to 95% ee). Furthermore, the substrate scope could be successfully extended to a range of phenols and alcohols with high yield (up to 92%) and excellent enantioselectivity (up to 97%) under mild reaction conditions. Additionally, a density functional theory (DFT) study was performed to elucidate the reaction mechanism.magnified image

Use of the Trost Ligand in the Ruthenium‐Catalyzed Asymmetric Hydrogenation of Ketones

AbstractThe Trost ligand, (1S,2S)‐1,2‐diaminocyclohexane‐N,N′‐bis(2′‐diphenylphosphinobenzoyl) (L), is reported for the first time as a ligand for the asymmetric hydrogenation (AH) of ketones. Ligand (S,S)‐L was screened in the presence of several metal salts and was found to form active catalysts if combined with ruthenium sources in the presence of hydrogen and a base. Reaction optimization was performed by screening different Ru sources, solvents, and bases. Under the optimized conditions, the complex formed by the combination of (S,S)‐L with RuCl3(H2O)x in the presence of Na2CO3 was able to promote the AH of several ketones at room temperature in good yields with up to 96 % ee. The reaction kinetics measured under the optimized conditions revealed the presence of a long induction period, during which the initially formed Ru species was transformed into the catalytically active complex by reaction with hydrogen. Remarkably, a ketone that is a precursor of the antiemetic drug aprepitant was hydrogenated in excellent yield with a good ee value.

Rhodium/Silver Synergistic Catalysis in Highly Enantioselective Cycloisomerization/Cross Coupling of Keto-Vinylidenecyclopropanes with Terminal Alkynes

A rhodium/silver synergistic catalysis has been established, enabling cycloisomerization/cross coupling of keto-vinylidenecyclopropanes (VDCPs) with terminal alkynes toward the regio- and enantioselective formation of diversified tetrahydropyridin-3-ol tethered 1,4-enynes in good yields and high ee values. In this synergistic catalysis, Rh(I) and Ag(I) catalysts selectively activate keto-VDCP substrates and terminal alkynes to generate the π-allyl Rh(III) complex of oxa-rhodacyclic intermediate and Ag alkynyl intermediate, respectively. The rapid transmetalation of alkynyl groups from Ag to Rh is proposed to play a key role in realizing the regioselective cleavage of the distal bond of the three-membered ring in this transformation.

N,N′‐Dioxide–Lanthanum(III)‐Catalyzed Asymmetric Cyclopropanation of 2‐Cyano‐3‐arylacrylates with 2‐Bromomalonates

AbstractAn efficient N,N′‐dioxide–lanthanum(III) complex catalytic system has been developed for the diastereo‐ and enantioselective Michael‐initiated ring‐closure (MIRC) reaction of 2‐cyano‐3‐arylacrylates with 2‐bromomalonates. Various chiral cyclopropanes with multiple substitutions were obtained in high yields (up to 93%) with excellent dr (>95:5 dr) and good ee values (up to 91% ee). The catalytic system also worked for the tandem halogenation/asymmetric MIRC reaction of α,β‐unsaturated nitriles, malonates and NBS. Besides, a possible catalytic model has been proposed to explain the origin of the stereoselectivity.magnified image

P(O)R2-Directed Enantioselective C-H Olefination toward Chiral Atropoisomeric Phosphine-Olefin Compounds.

An effective synthesis of chiral atropoisomeric biaryl phosphine-olefin compounds via palladium-catalyzed enantioselective C-H olefination has been developed for the first time. The reactions are operationally simple, tolerate wide functional groups, and have a good ee value. Notably, P(O)R2 not only acts as the directing group to direct C-H activation in order to make a useful ligand but also serves to facilitate composition of the product in a useful manner in this transformation.

Ken Tanaka

Ken Tanaka

One-pot synthesis of α,β-epoxy ketones through domino reaction between alkenes and aldehydes catalyzed by proline based chiral organocatalysts.

Proline based metal free organocatalysts were developed by using a new approach for the synthesis of epoxide derivatives through a domino reaction. This domino reaction (oxidative coupling) allows a direct access to epoxides from various alkenes and aldehydes through C-H functionalization and C-C/C-O bond formation. The catalytic efficiencies of the newly synthesized organocatalysts were also determined by domino reaction in the presence of various functional groups containing aldehyde and alkene derivatives with very good yields (up to 95%) and ee's (up to 99%).

Chiral N,N'-dioxide-Sc(NTf2)3 complex-catalyzed asymmetric bromoamination of chalones with N-bromosuccinimide as both bromine and amide source.

The catalytic asymmetric bromoamination of chalcones with N-bromosuccinimide as both bromine and amide source was realized by using a chiral N,N'-dioxide-Sc(NTf2)3 complex as an efficient catalyst. The corresponding chiral bromoamination products were obtained in high yields with high dr and good ee values (up to 92% yield, 93 : 7 dr and 97% ee) under mild reaction conditions.

ChemInform Abstract: Enantioselective Synthesis of Quaternary α‐Amino Acids via L‐tert‐Leucine‐Derived Squaramide‐Catalyzed Conjugate Addition of α‐Nitrocarboxylates to Enones.

Enantioselective Michael addition of tertiary α-nitroesters to β-unsubstituted vinyl ketones has been carried out in the presence of an l-tert-leucine-derived squaramide as organocatalyst. The products, quaternary α-nitroesters, were formed in excellent yield and moderate to good ee’s in most cases. Scale-up of the reaction and synthetic applications of the products, including transformation to representative quaternary α-amino acids, have also been demonstrated.

ChemInform Abstract: Rhodium‐Catalyzed Asymmetric [2 + 2 + 2] Cycloaddition of α,ω‐Diynes with Unsymmetrical 1,2‐Disubstituted Alkenes.

It has been established that a cationic rhodium(I)/axially chiral biaryl bisphosphine complex catalyzes the asymmetric [2 + 2 + 2] cycloaddition of α,ω-diynes with electron-rich and unstrained unsymmetrical 1,2-disubstituted alkenes to give chiral multicyclic compounds with good yields and ee values. Interestingly, enantioselectivity highly depends on the structures of α,ω-diynes used presumably due to the presence of two distinct reaction pathways.