Chiral Α-sulfinyl Research Articles

ChemInform Abstract: Role of Heterocycles on the Stereoselective Reactions of α- Sulfinyl Carbanions Using Optically Active 2-Pyridylmethyl p-Tolyl and 2-(N-Methylimidazolyl)methyl p-Tolyl Sulfoxides with Aldehydes.

Optically active 2-pyridylmethyl p-tolyl (1) and 2-(N-methylimidazolyl)methyl p-tolyl sulfoxides (2) were synthesized and the reactions of their chiral α-sulfinyl carbanions with aldehydes afforded stereoselectively the condensation products. The absolute configurations of the products were determined by X-ray crystallographic analysis and chemical reactions. The mechanism for the reactions is described

Asymmetric Synthesis of γ-Hydroxy α-Enones by 1,8-Diazabicyclo[5.4.0]undec-7-ene-Catalyzed Stereoselective Rearrangement of Chiral α-Sulfinyl Enones

The asymmetric rearrangement of optically active alpha-sulfinyl enone 1 induced by catalytic DBU and triphenylphosphine gave optically active gamma-hydroxy alpha-enone derivatives (up to 99% ee) in good yield following treatment with aqueous hydrogen peroxide.

Diastereofacial selectivity in aldol-type condensation induced by optically pure α-sulfinyl acetate with α-substituted aldehydes

Highly diastereoselective aldol-type condensations induced by the chiral magnesium enolate of tert-butyl p-tolyl sulfinyl acetate were performed with optically pure alkyl or hydroxy α-substituted aldehydes. The addition of chiral α-sulfinyl acetate to various aldehydes, α-substituted or not, results mainly with a syn stereochemistry of the two newly created stereocenters. Applications were investigated for the synthesis of syn and trans 1,2-diol models and polysubstituted precursor for natural products.

An improved method for the asymmetric protonation of enolates with chiral α-sulfinyl alcohols/trifluoroethanol

Enantioselective protonation of 2-methyl tetralone enolate using a stoichiometric amount of 2-sulfinyl alcohol ( S, R s)- 1 as a chiral proton donor yields the corresponding chiral ketone with a high level of enantioselectivity, provided that the chiral proton donor (CPD) is regenerated with an achiral proton source (APS). In contrast, stereoselectivity was only moderate if catalytic CPD (0.2 equiv.) and an APS are used.

Stereochemistry of transition metal catalyzed asymmetric intramolecular allyl transfer in chiral α-sulfinyl allylic esters

The stereochemistry of palladium or nickel catalyzed asymmetric intramolecular allyl transfer in chiral α-sulfinyl allylic esters was determined. The participation of the catalyst and the chiral sulfinyl functionality in these transformations, presumably by the coordination of the sulfinyl group to the catalyst, is discussed, and a novel mechanism is proposed for the rationalization of the results obtained.

Efficient asymmetric protonation of enolates with readily accessible chiral α-sulfinyl alcohols

The efficient asymmetric protonation of lithium enolates of 2-alkylcycloalkanones (87–96% ee) with readily accessible chiral α-sulfinyl alcohols is described. Optimal stereoselection is achieved for each lithium enolate at a different reaction temperature in the range −40 to −100°C.

Diastereofacial control in the radical addition to chiral α-sulfinyl enones

Abstract

Asymmetric desymmetrization of σ-symmetrical diols: the role of chelation in the diastereoselective acetal cleavage induced by the chiral α-sulfinyl carbanion

The reaction mechanism of β-elimination in α-sulfinyl acetals was investigated using the chiral 3-oxo-thiochroman-1-oxide derivatives 1a and 1b. Our results show that the reaction is kinetically controlled with the CO bond syn to the sulfinyl oxygen being cleaved exclusively. This reaction seems to proceed via six-membered ring chelation intermediates.

Asymmetric Desymmetrization of Prochiral 1,3-Diols via Diastereoselective C-O Bond Fission of Bicyclic Acetal Using a Chiral Sulfoxide as a Chiral Auxiliary.

Asymmetric desymmetrization of a prochiral 1, 3-diol was established by diastereoselective C-O bond fission of the chiral α-sulfinyl acetal 6. Treatment of 6 with titanium tetrachloride afforded mainly 7a via an oxonium intermediate, while with lithium diisopropylamide 7b was selectively obtained via diastereoselective β-elimination followed by an olefin isomerization.

Double diastereodifferentiation in the hydroxylative knovenagel condensation

The stereoinduction in formation of γ-hydroxy-α,β-unsaturated enoates using chiral α-sulfinyl esters and chiral aldehydes is a function of the absolute stereochemistry of the sulfoxide, the substituent on the sulfoxide, and the amount of base.

Conjugate-addition reactions of .alpha.-sulfinyl ketimine anions with a methyl .alpha.-amidoacrylate. Concise asymmetric total syntheses of (-)-slaframine and (-)-6-epislaframine

The in-situ 1,4-addition/ring-closure reactions of chiral α-sulfinyl ketimine anions with a methyl α-amidoacrylate provide a simple method for the construction of optically pure 6-aminoindolizidinones. This method afforded the syntheses of (-)-slaframine and (-)-6-epislaframine in six steps, respectively, from (±)-3-[(tert-butyldimethylsilyl)oxy]-4,5-dihydro-2-methyl-3H-pyrrole (9). Stereoselective reductions of α-sulfinyl ketimines (such as 10) were also developed

Studies on Chiral Organosulfur Compounds. III. Lewis Acid-Catalyzed Intramolecular Asymmetric Pericyclic Reactions of Chiral .ALPHA.-Acetyl and Methoxycarbonylvinylic Sulfoxides.

A chiral α-sulfinyl α, β-unsaturated ketone served as a good chiral diene or enophile in intramolecular Lewis acid-catalyzed asymmetric pericyclic reactions, giving hetero-Diels-Alder reaction products, together with ene reaction products in some cases, in high optical yields. The reaction pathways for Diels-Alder or ene reactions were readily controlled depending on the Lewis acids used. A chiral α-sulfinyl α, β-unsaturated ester served as a good enophile to give ene reaction products with high enantioselectivity. The mechanistic pathway for the asymmetric induction is proposed on the basis of the stereochemical results obtained.

Intramolecular Lewis acid-catalyzed asymmetric hetero-Diels-Alder reactions with dienes bearing chiral sulfinyl groups

A chiral α-sulfinyl α,β-unsaturated ketone served as a chiral diene in intramolecular Lewis acid-catalyzed asymmetric cycloaddition reactions, giving hetero-Diels-Alder reaction products along in some cases with ene reaction products in high optical yields. The reaction pathways for Diels-Alder or ene reactions were readily controlled depending on the Lewis acids used.

ChemInform Abstract: Stereoselective Additions of Chiral α‐Sulfinyl Ketimine Anions to Ene Esters. Asymmetric Syntheses of Indolo(2,3‐a)quinolizidine and Yohimban Alkaloids.

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Role of Heterocycles on the Stereoselective Reactions of a-Sulfinyl Carbanions Using Optically Active 2-Pyridylmethyl p-Tolyl and 2-(N-Methylimidazolyl)methyl p-Toyl Sulfoxides with Aldehydes

Optically active 2-pyridylmethyl p-tolyl (1) and 2-(N-methylimidazolyl)methyl p-tolyl sulfoxides (2) were synthesized and the reactions of their chiral α-sulfinyl carbanions with aldehydes afforded stereoselectively the condensation products. The absolute configurations of the products were determined by X-ray crystallographic analysis and chemical reactions. The mechanism for the reactions is described

Induction asymetrique lors de l'addition de Michael d'un ester α-sulfinyle chiral

During the Michael addition of chiral α-sulfinyl eser (+) 1 R on αβ-unsaturated esters, an extent of 24% of asymmetric induction was observed. It is shown that the addition products can be transformed into optically active δ-lactones.