Cyclic Meso Research Articles

Interconversion of tetrahedral [(M)4∩{Mg4(L1)6}]/[In4(L2)4] and cyclic [In6Cl6(L3)6]. Enantiotopization of diastereotopic protons monitored by means of VT 1H NMR spectroscopy

AbstractIn this review we report on the enantiomerization of tetrahedral racemic‐[(NH4)4∩{Mg4(L1)6}] monitored by means of variable temperature (VT) 1H NMR spectroscopy. The enantiotopization of the diastereotopic protons is due to simultaneous Bailar twists at the four octahedrally coordinated magnesium centres, synchronized with atropisomerization of the six edge‐bridging ligands (L1)2‐.The VT 1H NMR spectrum of tetrahedral meso‐[In4(L2)4] is coined through the helicity of the four face‐centred tripodal hexadentate ligands (L2)3‐ and can, alike the 1H NMR of cyclic meso‐[In6Cl6(L3)6], be explained by the enantiotopization of the diastereotopic protons via mesomerization.

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.

ChemInform Abstract: Enantioselective Fluoride Ring Opening of Aziridines Enabled by Cooperative Lewis Acid Catalysis.

AbstractThe first enantioselective fluoride ring opening of acyclic and cyclic meso N‐picolinamide aziridines using a latent source of HF is described.

Enantioselective fluoride ring opening of aziridines enabled by cooperative Lewis acid catalysis

The enantioselective ring opening of aziridines using a latent source of HF is described. A combination of two Lewis acids, (salen)Co and an achiral Ti(IV) cocatalyst, provided optimal reactivity and enantioselectivity for the trans β-fluoroamine product. The use of a chelating aziridine protecting group was crucial. Acyclic and cyclic meso N-picolinamide aziridines underwent fluoride ring opening in up to 84% ee, and the kinetic resolution of a piperidine-derived aziridine was performed with krel=6.6. The picolinamide group may be readily removed without epimerization of the fluoroamine. Preliminary studies revealed a bimetallic mechanism wherein the chiral (salen)Co catalyst delivers the nucleophile and the Ti(IV) cocatalyst activates the aziridine.

ChemInform Abstract: Enantioselective Nucleophilic Opening of meso Epoxides by Organolithium Reagents.

Aryl lithium reagents, complexed with (-)-sparteine, react enantioselectively with cyclic meso epoxides, to afford chiral aryl cyclanols. The enantiomeric excess, though moderate (27-87%), is the best in the literature for such a reaction. Activation by BF3 · OEt2 is needed, and is compatible with a diamine such as (-)-sparteine.

A Concise Synthesis of Eupomatilones 4, 6, and 7 by Rhodium‐Catalyzed Enantioselective Desymmetrization of Cyclic meso Anhydrides with Organozinc Reagents Generated in situ.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Asymmetric desymmetrization of meso- vic-diols by carbamoylation catalyzed with a chiral Cu(II) complex

Asymmetric desymmetrization of meso- vic-diols was achieved by carbamoylation in the presence of copper triflate and ( S, S)-Ph-BOX as a catalyst without any use of bases. The method was successfully applied to asymmetric desymmetrization of five- to eight-membered cyclic meso- vic-diols in high enantioselectivity with up to 93% ee.

Palladium‐Catalyzed One‐Step Preparation of Novel Tricyclic Phenoxazine, Phenazine, and Dioxine Derivatives

AbstractFor Abstract see ChemInform Abstract in Full Text.

Palladium-Catalyzed One-Step Preparation of Novel Tricyclic Phenoxazine, Phenazine, and Dioxine Derivatives

Reaction of cyclic meso allylic diacetates 5 and 6 with various 2-aminophenols, benzene-1,2-diamine, and benzene-1,2-diol in the presence of a palladium-phosphine catalyst gave novel phenoxazine, phenazine, and dioxine derivatives 7, 11, and 12 in moderate to excellent yields.

Study on enantiomerically pure 2-substituted N, N-dialkyl-1-naphthamides: resolution, absolute stereochemistry, and application to desymmetrization of cyclic meso anhydrides

The axially chiral 2-substituted N, N-diisopropyl-1-naphthamides 1 and 2 were resolved by HPLC over a chiral stationary phase to provide enantiomerically pure atropisomers. The absolute stereochemistry of (−)- syn- 1 was determined by X-ray crystallographic analysis of the corresponding (1 S)-camphanic acid ester derivative. Desymmetrization of cyclic meso anhydrides 5a and 5b using (−)- syn- 1 gave a single diastereomer in good yield.

Enantioselective Nucleophilic Opening of meso Epoxides by Organolithium Reagents

Aryl lithium reagents, complexed with (-)-sparteine, react enantioselectively with cyclic meso epoxides, to afford chiral aryl cyclanols. The enantiomeric excess, though moderate (27-87%), is the best in the literature for such a reaction. Activation by BF3 · OEt2 is needed, and is compatible with a diamine such as (-)-sparteine.

Highly Enantioselective Ring Opening of CyclicMeso-Anhydrides to Isopropyl Hemiesters with Ti−TADDOLates: An Alternative to Hydrolytic Enzymes?

The Lewis acid mediated transfer of an alkoxide ligand from the chiral ligand sphere of Ti−TADDOLate (1) to cyclic meso anhydrides to afford the corresponding hemiesters is described. By using this method a variety of structurally different anhydrides can be converted to isopropyl hemiesters with high enantioselectivities (enantiomer ratios up to 99:1). We have also investigated Lewis acidic titanium complexes, which differ from 1 in the chiral ligand or the alkoxide ligand that is transferred. Finally, a catalytic version, which allows the substoichiometric use of Ti−TADDOLate in the presence of stoichiometric amounts of Al(Oi-Pr)3, is presented.

ChemInform Abstract: Enzymes in Organic Synthesis. Part 39. Preparations of Chiral Cyclic Acid‐Esters and Bicyclic Lactones via Stereoselective Pig Liver Esterase Catalyzed Hydrolyses of Cyclic Meso Diesters.

ChemInform Abstract: Enzymes in Organic Synthesis. Part 39. Preparations of Chiral Cyclic Acid‐Esters and Bicyclic Lactones via Stereoselective Pig Liver Esterase Catalyzed Hydrolyses of Cyclic Meso Diesters.

Enzymes in organic synthesis. 39. Preparations of chiral cyclic acid-esters and bicyclic lactones via stereoselective pig liver esterase catalyzed hydrolyses of cyclic meso diesters

Enzymes in organic synthesis. 39. Preparations of chiral cyclic acid-esters and bicyclic lactones via stereoselective pig liver esterase catalyzed hydrolyses of cyclic meso diesters