Asymmetric Desymmetrization Research Articles

Construction of 2‐Thiabicyclo[3.3.1]nonanes by Organocatalytic Asymmetric Formal [3+3] Cycloaddition

Powerful asymmetric desymmetrization of thiane‐3,5‐diones through formal [3+3] cycloaddition with alkyl vinyl ketones has been disclosed to access functionally rich 2‐thiabicyclo[3.3.1]nonanes in very good yields with excellent enantio‐ and diastereoselectivities by using organocatalysis.

Catalytically Enantioselective Synthesis of Acyclic α-Tertiary Amines through Desymmetrization of 2-Substituted 2-Nitro-1,3-diols.

Highly enantioselective synthesis of acyclic α-tertiary amines through asymmetric desymmetrization is reported. This approach is based on chiral phosphoric acid mediated, enantioselective, oxidative desymmetrization of 2-substituted 2-nitro-1,3-diolbenzylidine acetals in the presence of DMDO as an oxidant. The method allows for the formation of a wide variety of chiral 2-nitro-1,3-diols in high enantioselectivity, which could be transformed into optically pure, unnatural α-alkyl series. The synthetic utility of this method has been further demonstrated by the expedient construction of the core structure of natural products manzacidins enantioselectively.

Desymmetrizing Enantio- and Diastereoselective Selenoetherification through Supramolecular Catalysis

Selenofunctionalization is used for the introduction of aryl- or alkylseleno moieties, which can then be transformed into other functional groups (such as alkenes and carbonyls). However, asymmetric selenofunctionalization of unactivated olefins is often difficult to realize, as aryl- and alkylseleno cations rapidly interchange between olefinic partners. Recently, it has been demonstrated that Lewis bases, assisted by Bronsted acids, induce high levels of enantioselectivity in selenocyclization reactions. The Bronsted acid serves as an activator for the reaction. In this work, we demonstrate an asymmetric selenoetherification and desymmetrization of olefinic 1,3-diols, driven by a unique chiral pairing between a C2-symmetric cyclic selenide catalyst and a chiral Bronsted acid. The resulting substituted tetrahydrofurans contain a phenylselenoether handle and can be transformed into synthetically useful building blocks. A series of experimental and computational investigations suggest that the reaction proc...

Asymmetric synthesis of functionalized tetrahydrofluorenones via an NHC-catalyzed homoenolate Michael addition.

The first example of an N-heterocyclic carbene-catalyzed asymmetric desymmetrization of enal-tethered cyclohexadienones via an intramolecular homoenolate Michael addition/esterification reaction is described. This new protocol offers a direct entry to various functionalized tetrahydrofluorenones with three contiguous stereocenters in high yields, good diastereoselectivities and excellent enantioselectivities.

Enantioselective Palladium-Catalyzed Intramolecular α-Arylative Desymmetrization of 1,3-Diketones

An efficient enantioselective protocol has been reported to build highly oxygenated and densely substituted bicyclo[m.n.1] skeletons through intramolecular asymmetric α-arylative desymmetrization of 1,3-diketones. Employing Pd catalyst and FOXAP ligand, various bicyclo[m.n.1] skeleton with different size can be accessed with high enantio- and diastereoselectivities. Utilizing the present method as a key step, formal asymmetric total synthesis of the (-)-parvifoline has been demonstrated.

Asymmetric Nickel-Catalyzed Desymmetrization Reaction

Key words nickel catalysis - asymmetric desymmetrization - 1,6-stereocenters

Catalytic Asymmetric Desymmetrization of Cyclopentendiones via Diels-Alder Reaction of 3-Hydroxy-2-pyrones: Construction of Multifunctional Bridged Tricyclic Lactones.

An unprecedented asymmetric Diels-Alder reaction of 3-hydroxy-2-pyrones with prochiral cyclopentene-1,3-diones via desymmetrization was efficiently realized with high stereoselective control with the aid of fine-tunable cinchona alkaloid derived bifunctional amine-thiourea catalysts bearing multiple hydrogen-bonding donors. This protocol provides an expedient access to the multifunctional-bridged tricyclic lactones featuring four contiguous stereogenic centers and one remote quaternary stereogenic center with a broad substrate scope. The cycloadduct can be readily elaborated into enantioenriched cyclopentane-1,3-diones via ring opening/aromatization.

Asymmetric Desymmetrization of Substituted Cyclohexadienones by Rhodium-Catalyzed Conjugate Hydrosilylation and Theoretical Calculations of Its Mechanistic Aspects

Asymmetric desymmetrization was demonstrated by means of transition-metal-catalyzed conjugate reduction with hydrosilanes as reductants. Chiral rhodium-bis(oxazolinyl)phenyl complexes [Rh(Phebox-R)] were found to be effective catalysts for conjugate hydrosilylation of differently γ,γ-disubstituted cyclohexadienones to provide the corresponding product with chiral quaternary centers. The mechanistic consideration was also performed by theoretical calculation. These attempts provided information about i) the initial activation of Rh(III) complex into Rh(I) species assisted by hydrosilanes, ii) the complete catalytic cycle, and iii) an explanation of the asymmetric induction and the difference of the structure of cyclohexadienones in enantioselectivity.

Asymmetric Desymmetrization of Silylcyclopentadiene with Azoalkene

Key words copper catalysis - aza-Diels–Alder reaction - desymmetrization - inverse electron demand - tetrahydro-pyridazines

Reactivity of Grubbs–Hoveyda II Complexes Including Extended N-Heterocyclic Carbenes with a Bicyclic Camphor-Based Framework

This feature article discusses the synthesis of new asymmetric Grubbs–Hoveyda II complexes with extended N-heterocyclic carbenes containing a bicyclic camphor-based framework. The new enantiopure complexes can be prepared in a short route from the chiral pool. The extended carbene-based catalyst shows high activity in olefin metathesis reactions. The new complexes exhibited enantioselectivity in an asymmetric ROCM desymmetrization. Depending on the substituents on the nitrogen atoms of the carbenes, the opposite enantiomer was formed in excess.

Copper(I)-Catalyzed Asymmetric Desymmetrization through Inverse-Electron-Demand aza-Diels-Alder Reaction: Efficient Access to Tetrahydropyridazines Bearing a Unique α-Chiral Silane Moiety.

An unprecedented copper(I)-catalyzed asymmetric desymmetrization of 5-silylcyclopentadienes with in situ formed azoalkene was realized through an inverse-electron-demand aza-Diels-Alder reaction (IEDDA) pathway, in which 5-silylcyclopentadienes served as efficient enophiles. This new protocol provides a facile access to the biologically important heterocyclic tetrahydropyridazines containing a unique α-chiral silane motif and three adjoining stereogenic centers in generally good yield (up to 92 %) with exclusive regioselectivity, high diastereoselectivity (>20:1 diastereomeric ratio), and excellent enantioselectivity (up to 98 % enantiomeric excess). DFT calculations and control experiments further confirmed the proposed reaction mechanism.

Enantioselective Synthesis of Chiral Oxygen-Containing Heterocycles Using Copper-Catalyzed Aryl C-O Coupling Reactions via Asymmetric Desymmetrization.

An enantioselective desymmetric aryl C-O coupling reaction was demonstrated under the catalysis of CuI and a chiral cyclic diamine ligand. A series of chiral oxygen-containing heterocyclic units such as 2,3-dihydrobenzofurans, chromans, and 1,4-benzodioxanes with tertiary or quaternary stereocarbon centers were synthesized with this method. DFT calculations were also carried out for a better understanding of the model for enantiocontrol.

A Theoretical Mechanistic Study of the Asymmetric Desymmetrization of a Cyclic meso-Anhydride by a Bifunctional Quinine Sulfonamide Organocatalyst.

Cinchona alkaloids and their derivatives are widely used as organocatalysts in asymmetric synthesis. In particular, sulfonamide derivatives of cinchona alkaloids are highly enantioselective desymmetrization catalysts in the ring opening of a variety of cyclic anhydrides. To better understand the mechanism of catalysis, as well as to identify the basis for enantioselectivity by this catalyst, we have performed DFT calculations of this reaction with a cyclic meso anhydride. Herein, we report calculations for two reaction pathways, one concerted and one stepwise, for the production of each enantiomer of the desymmetrized product using the complete sulfonamide catalyst I. Our results are consistent with both the enantioselectivity of this transformation and the catalytic role of the quinuclidine moiety. We find that the stepwise pathway is the relevant pathway in the production of the major enantiomer. Our calculations highlight the role of differential distortion of the anhydride-methanol complex in the transition state as the factor leading to stereoselectivity.

The Construction of Chiral Fused Azabicycles Using a Pd-Catalyzed Allylic Substitution Cascade and Asymmetric Desymmetrization Strategy.

A highly enantioselective Pd-catalyzed asymmetric allylic substitution cascade of cyclic N-sulfonylimines with an accompanying asymmetric desymmetrization has been developed for the construction of fused tetrahydroindole derivatives bearing two chiral centers. Mechanistic studies confirmed that the cascade reaction proceeds by initial allylic alkylation and subsequent allylic amination. The first alkylation is a chirality-control step and represents an asymmetric desymmetrization of cis-cyclic allyl diacetates. The reaction has been performed on a gram scale, and the desired products can take part in several transformations.

Synthesis of Chiral Vicinal Diamines by Silver(I)‐Catalyzed Enantioselective Aminolysis of N‐Tosylaziridines

AbstractThe kinetic resolution of 2‐aryl‐N‐tosylaziridines and the asymmetric desymmetrization of meso‐N‐tosylaziridines by ring openings with various primary and secondary anilines, and aliphatic amines as nucleophile have been realized by using a single silver(I)/chiral diphosphine complex as catalyst for the first time. The simple starting materials, broad scope, and easy scalability render this protocol a practical way to chiral vicinal diamine derivatives.

Synthesis of Chiral Vicinal Diamines by Silver(I)-Catalyzed Enantioselective Aminolysis of N-Tosylaziridines.

The kinetic resolution of 2-aryl-N-tosylaziridines and the asymmetric desymmetrization of meso-N-tosylaziridines by ring openings with various primary and secondary anilines, and aliphatic amines as nucleophile have been realized by using a single silver(I)/chiral diphosphine complex as catalyst for the first time. The simple starting materials, broad scope, and easy scalability render this protocol a practical way to chiral vicinal diamine derivatives.

Catalytic Enantioselective Synthesis of N-C Axially Chiral Mebroqualone and Its Derivatives through Reductive Asymmetric Desymmetrization.

In the presence of (R)-DTBM-SEGPHOS-Pd(OAc)2 catalyst, treatment of various 3-(2,6-dibromophenyl)quinazolin-4-ones with NaBH4 gave optically active N-C axially chiral quinazolinone (mebroqualone) derivatives through reductive asymmetric desymmetrization (enantioselective monohydrodebromination) followed by kinetic resolution of the resulting monobromophenyl products (up to 99% ee). The enantioselectivity strongly depended on the substituent (R2) at the C4'position, amount of NaBH4, and reaction temperature.

ChemInform Abstract: Ru‐Catalyzed Asymmetric Hydrogenative/Transfer Hydrogenative Desymmetrization of Meso‐Epoxy Diketones.

Via a strategy of asymmetric reductive desymmetrization, chiral cis-epoxy naphthoquinols with multiple contiguous stereocenters and functional groups were synthesized with excellent enantioselectivities (96–99% ee) and diastereoselectivities (8/1–15/1). A combined asymmetric hydrogenation/transfer hydrogenation mechanism was proposed based on experimental results.

ChemInform Abstract: N‐Heterocyclic Carbene‐Catalyzed Desymmetrization of Functionalized 1,4‐Dienes via Stetter Reaction.

The asymmetric desymmetrization of 1,4-dienes via chiral N-heterocyclic carbene catalyzed Stetter-type umpolung reaction was demonstrated. A variety of differently substituted dienes were tolerated very well, affording cyclic ketones with two consecutive stereogenic centers (including one quaternary carbon) in moderate to high yields and with high to excellent enantioselectivities. This work expanded both reaction types of catalytic diene desymmetrizations and substrate diversity in NHC catalyzed desymmetric transformations.

ChemInform Abstract: Dysprosium(III)‐Catalyzed Ring‐Opening of meso‐Epoxides: Desymmetrization by Remote Stereocontrol in a Thiolysis/Elimination Sequence.

AbstractThis unprecedented asymmetric desymmetrization of meso‐epoxides with mercaptobenzothiazoles is catalyzed by a chiral Dy(III)/N,N‐dioxide complex through a thiolysis/elimination sequence.