Enantioselective Ring-opening Reaction Research Articles

Catalytic Asymmetric Ring-Opening Reactions of Unstrained Heterocycles Using Cobalt Vinylidenes.

Cobalt catalysts promote highly enantioselective ring-opening reactions of 2,5-dihydrofurans using vinylidenes. The products are acyclic organozinc compounds that can be functionalized with an electrophile. The proposed mechanism involves the generation of a cobalt vinylidene species that adds to the alkene by a [2+2]-cycloaddition pathway. Ring-opening then occurs via outer-sphere β-O elimination assisted by coordination of a ZnX2 Lewis acid to the alkoxide leaving group. DFT models reveal that competing inner-sphere syn β-H and β-O elimination pathways are suppressed by the geometric constraints of the metallacycle intermediate. These models rationalize the observed stereochemical outcome of the 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.

Nickel-Catalyzed Regio- and Enantioselective Ring Opening of 3,4-Epoxy Amides and Esters with Aromatic Amines.

Herein we present a nickel-catalyzed regio- and enantioselective ring opening reaction of 3,4-epoxy amides and esters with aromatic amines as nucleophiles. This method features high regiocontrol, diastereospecific SN 2 reaction pathway, broad substrate scope, and mild reaction conditions, furnishing a wide range of γ-amino acid derivatives in a highly enantioselective manner. Notably, the selective nucleophilic attack to the C-4 position of epoxides is controlled by the directing effect of the pendant carbonyl group.

Biocatalytic Thionation of Epoxides for Enantioselective Synthesis of Thiiranes.

Expanding the enzymatic toolbox for the green synthesis of valuable molecules is still of high interest in synthetic chemistry and the pharmaceutical industry. Chiral thiiranes are valuable sulfur-containing heterocyclic compounds, but relevant methods for their enantioselective synthesis are limited. Herein, we report a biocatalytic thionation strategy for the enantioselective synthesis of thiiranes, which was developed based on the halohydrin dehalogenase (HHDH)-catalyzed enantioselective ring-opening reaction of epoxides with thiocyanate and a subsequent nonenzymatic rearrangement process. A novel HHDH was identified and engineered for enantioselective biocatalytic thionation of various aryl- and alkyl-substituted epoxides on a preparative scale, affording the corresponding thiiranes in up to 43 % isolated yield and 98 % ee. Large-scale synthesis and useful transformations of chiral thiiranes were also performed to demonstrate the utility and scalability of the biocatalytic thionation strategy.

Diols Activation by Cu/Borinic Acids Synergistic Catalysis in Atroposelective Ring-Opening of Cyclic Diaryliodoniums.

A Cu-catalyzed enantioselective ring-opening alkoxygenation reaction of cyclic diaryliodonium salts and diols in the presence of borinic acids was reported. Tuning structure of borinic acids with six or five-membered ring skeleton could selectively activate 1,2-diols or 1,4-diols. A catalytic cycle through a key ion pair model that accounts for the observed enantioselectivity was proposed.

Enantioselective preparation of atropisomeric biaryl trifluoromethylsulfanes via ring-opening of cyclic diaryliodoniums.

Two convenient and practical methods for the synthesis of axially chiral biaryls bearing the trifluoromethylthio group are reported. A Cu-catalyzed enantioselective ring-opening reaction of cyclic diaryliodoniums with CsSCF3 enables the direct synthesis of trifluoromethylthiolated biaryl atropisomers in high yields and enantioselectivity. For unsymmetric cyclic diaryliodoniums bearing an adjacent group to the C-I bond, a two-step procedure is required to achieve good regio- and enantioselectivity.

Regio- and enantioselective ring-opening reaction of vinylcyclopropanes with indoles under cooperative catalysis

The title reaction has been established under the cooperative bimetallic catalysis of iridium and copper catalysts, which afforded indole C3-allylation products with branched selectivity in moderate yields and good enantioselectivities.

Atroposelective Ring Opening of Cyclic Diaryliodonium Salts with Bulky Anilines Controlled by a Chiral Cobalt(III) Anion

AbstractThe present work demonstrates a CuCl and anionic chiral cobalt(III)‐catalyzed enantioselective ring‐opening reaction. The small‐size, ligand‐free copper species enabled the cross‐coupling of iodonium salts with a series of bulky aromatic amines in high ee values. The chiral cobalt(III) anion causes appreciable chemical shift changes of cyclic diaryliodoniums in 1H NMR spectra.

Atroposelective Ring Opening of Cyclic Diaryliodonium Salts with Bulky Anilines Controlled by a Chiral Cobalt(III) Anion.

The present work demonstrates a CuCl and anionic chiral cobalt(III)-catalyzed enantioselective ring-opening reaction. The small-size, ligand-free copper species enabled the cross-coupling of iodonium salts with a series of bulky aromatic amines in high ee values. The chiral cobalt(III) anion causes appreciable chemical shift changes of cyclic diaryliodoniums in 1 H NMR spectra.

Catalytic Enantioselective Ring-Opening Reactions of Cyclopropanes.

This review describes the development of enantioselective methods for the ring opening of cyclopropanes. Both approaches based on the reaction of nonchiral cyclopropanes and (dynamic) kinetic resolutions and asymmetric transformations of chiral substrates are presented. The review is organized according to substrate classes, starting by the more mature field of donor-acceptor cyclopropanes. Emerging methods for enantioselective ring opening of acceptor- or donor-only cyclopropanes are then presented. The last part of the review describes the ring opening of more reactive three-membered rings substituted with unsaturations with a particular focus on vinylcyclopropanes, alkylidenecyclopropanes, and vinylidenecyclopropanes. In the last two decades, the field has grown from a proof of concept stage to a broad range of methods for accessing enantioenriched building blocks, and further extensive developments can be expected in the future.

Copper-Catalyzed Enantioselective Ring-Opening of Cyclic Diaryliodoniums and O-Alkylhydroxylamines.

A preparation of 2-hydroxyamino-2'-iodobiaryls via the Cu-catalyzed enantioselective ring-opening reaction of cyclic diaryliodonium salts with O-alkylhydroxylamines is reported. 3,5-Di(tert-butyl)phenyl bis(oxazoline) was found to be the optimal ligand, and up to 99% ee values were achieved. The use of CaO as the base dramatically improved the yields and inhibited the side reactions. Finally, synthetic applications of these hydroxylamines were briefly demonstrated.

Copper-Catalyzed Asymmetric Aminocyanation of Arylcyclopropanes for Synthesis of γ-Amino Nitriles

A facile approach for the synthesis of enantiopure γ-amino nitriles by copper-catalyzed aminocyanation of arylcyclopropanes is disclosed, which undergoes the highly enantioselective ring-opening reaction of cyclopropanes. The strategy utilizes N-fluorobenzenesulfonimide as nucleophilic nitrogen source as well as oxidant and trimethylsilyl cyanide as the other nucleophile, and it probably operates via a key radical cation intermediate. This reaction provides an efficient platform for asymmetric 1,3-difunctionalization of cyclopropanes.

Enhanced Reactivity by Torsional Strain of Cyclic Diaryliodonium in Cu-Catalyzed Enantioselective Ring-Opening Reaction

Summary Atropisomers are stereoisomers arising from the restricted rotation around a single bond. In particular, biaryl atropisomers represent an important class of compounds, as they are widely present in natural products, ligands and pharmaceutical molecules. However, the preparation of structurally diverse biaryl atropisomers under mild conditions is a significant challenge. Here, we describe a Cu-bis(oxazolinyl)pyridine-catalyzed asymmetric ring-opening amination reaction of cyclic diaryliodoniums. Increasing the torsional strain of these cyclic compounds significantly improved the reactivity of cyclic diaryliodoniums. Computational investigation indicated that the two conformers of the cyclic diaryliodoniums had a low rotational barrier, and generally the reaction achieved high yields and high enantioselectivity (up to >99% ee). Furthermore, this ring-opening amination reaction also featured high atom economy in comparison with traditional reactions involving diaryliodonium. Finally, we propose a catalytic cycle and a mechanistic model that accounts for the observed enantioselectivity.

Enantioselective Ring Opening Reactions of Azabenzonorbornadienes with Carboxylic Acids

AbstractThe palladium/silver (Pd/Ag) co‐catalytic system was found to be effective for the enantioselective ring opening reactions of the low reactive azabenzonorbornadienes with weak nucleophilic carboxylic acids. Both aryl and alkyl carboxylic acids are suitable nucleophiles and afforded the cis ring opening products in good yields with excellent enantioselectivities. The absolute configuration of one of the products has been confirmed by X‐ray crystal structure analysis, and a plausible reaction pathway is proposed.magnified image

ChemInform Abstract: Asymmetric Ring‐Opening Reactions of Donor—Acceptor Cyclopropanes and Cyclobutanes

AbstractReview: [21 refs.

Microwave Specific Effect on Catalytic atropo-Enantioselective Ring-Opening Reaction of Biaryl Lactones

Abstract The microwave specific effect on the catalytic atropo-enantioselective ring-opening reaction of biaryl lactones was investigated. Under strictly controlled temperature conditions, the reaction was accelerated by microwave irradiation without any loss of the enantioselectivity. Also, the racemization rate of the atropo-optically active biaryl lactone was enhanced by the microwave irradiation.

Catalytic Asymmetric Ring-Opening Reactions of Aziridines with 3-Aryl-Oxindoles.

A highly enantioselective ring-opening alkylation reaction between 3-aryl-oxindole and N-(2-picolinoyl) aziridine has been realized for the first time. The reaction is efficiently mediated by a simple in-situ-generated magnesium catalyst and 3,3'-fluorinated-BINOL (BINOL=1,1'-binaphthalene-2,2'-diol) has been identified as a powerful chiral ligand. Notably, the fluorine atom on the chiral ligand plays a key role in providing the desired chiral 3-alkyl-3-aryl oxindoles with excellent enantioselectivities.

Asymmetric H2O-Nucleophilic Ring Opening of D-A Cyclopropanes: Catalyst Serves as a Source of Water.

The first catalytic enantioselective ring-opening reaction of donor-acceptor cyclopropanes with water is described. By employing Cy-TOX/Cu(II) as catalyst, the reaction performed very well over a broad range of substrates, leading to the ring-opening products in 70-96% yields with up to 95% ee under mild conditions. The current method provides a new approach to direct access to γ-substituted GBH derivatives very efficiently. Importantly, Cu(ClO4)2·6H2O proves to serve as both a Lewis acid and a source of water, which affords a fine system to controllably release water as a nucleophile in the asymmetric catalysis.

Iridium-catalyzed highly enantioselective ring opening reaction of oxabenzonorbornadienes with amines

The complex of [Ir(COD)Cl]2 and (R)-xylyl-phanephos was used as an effective catalyst for the asymmetric ring opening reaction of oxabenzonorbornadienes with various amines. Under the optimized reaction conditions, high enantioselectivities with moderate to good yields could be obtained from a wild scope of oxabenzonorbornadienes and amines.

ChemInform Abstract: Regio‐ and Enantioselective Friedel—Crafts Reactions of Indoles to Epoxides Catalyzed by Graphene Oxide: A Green Approach.

Graphene oxide efficiently promotes high regio- and enantioselective ring opening reactions of aromatic epoxides by indoles addition, in solvent- and metal-free conditions. The Friedel-Crafts products were obtained with enantioselectivity up to 99 % ee. The complete inversion of stereochemistry indicates the occurrence of SN 2-type reaction, which assures high level of enantioselectivity.