Browse
Submit Data
Databases
API
Help

Dataset Information

0 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Stereoselective conjugate radical additions: application of a fluorous oxazolidinone chiral auxiliary for efficient tin removal.

ABSTRACT: [reaction: see text] A series of asymmetric free-radical-mediated intermolecular conjugate additions using a fluorous oxazolidinone chiral auxiliary has been completed. The fluorous auxiliary facilitated product isolation using fluorous solid phase extractions (FSPE), effectively removing excess organic and organometallic reagents. Parallel reactions carried out with a similar but nonfluorous norephedrine-derived oxazolidinone demonstrated the superior stereoselectivity and purification obtainable with the fluorous chiral auxiliary.

SUBMITTER: Hein JE

PROVIDER: S-EPMC1524859 | biostudies-literature | 2005 Jun

REPOSITORIES: biostudies-literature

ACCESS DATA

Json Xml

Publications

Stereoselective conjugate radical additions: application of a fluorous oxazolidinone chiral auxiliary for efficient tin removal.

Hein Jason E JE Zimmerman Jake J Sibi Mukund P MP Hultin Philip G PG

Organic letters 20050601 13

[reaction: see text] A series of asymmetric free-radical-mediated intermolecular conjugate additions using a fluorous oxazolidinone chiral auxiliary has been completed. The fluorous auxiliary facilitated product isolation using fluorous solid phase extractions (FSPE), effectively removing excess organic and organometallic reagents. Parallel reactions carried out with a similar but nonfluorous norephedrine-derived oxazolidinone demonstrated the superior stereoselectivity and purification obtainab ...[more]

PMID: 15957939

Similar Datasets

Novel asymmetric photodimerization reaction of coumarin derivatives bearing a chiral 2-oxazolidinone auxiliary.

Project description:A novel asymmetric photodimerization reaction of coumarin derivatives bearing the (S)-4-benzyl-2-oxazolidinone auxiliary provides only the syn-head-to-tail (syn-HT) dimer with moderate diastereoselectivity (up to 75 : 25). The mechanism of complete syn-HT selectivity and moderate diastereoselectivity is proposed based on the result of density functional theory (DFT) calculation. The benzyl group of the (S)-4-benzyl-2-oxazolidinone auxiliary in combination with a Lewis acid exerts effective diastereofacial shielding of the reaction site.

| S-EPMC9063662 | biostudies-literature

Stereoselective RNA Reaction with Chiral 2'-OH Acylating Agents

Project description:The reactivity of RNA 2'-OH groups with acylating agents has recently been investigated for high-yield conjugation of RNA strands. To date, only achiral molecules have been studied for this reaction, despite the complex chiral structure of RNA. Here we prepare a set of chiral acylimidazoles and study their stereoselectivity in RNA reactions. Reactions performed with unfolded and folded RNAs reveal that positional selectivity and reactivity vary widely with local RNA macro-chirality. We further document remarkable effects of chirality on reagent reactivity, identifying an asymmetric reagent with 1000-fold greater reactivity than prior achiral reagents. In addition, we identify a chiral compound with higher RNA structural selectivity than any previously reported RNA-mapping species. Further, azide-containing homologs of a chiral dimethylalanine reagent were synthesized and applied to local RNA labeling, displaying 92% yield and 16:1 diastereoselectivity. The results establish that reagent stereochemistry and chiral RNA structure are critical elements of small molecule-RNA reactions, and demonstrate new chemical strategies for selective RNA modification and probing.

2023-11-14 | GSE247565 | GEO

An Auxiliary Approach for the Stereoselective Synthesis of Topologically Chiral Catenanes.

Project description:Catenanes, molecules in which two rings are threaded through one another like links in a chain, can form as two structures related like an object and its mirror image but otherwise identical if the individual rings lack bilateral symmetry. These structures are described as "topologically chiral" because, unlike most chiral molecules, it is not possible to convert one mirror-image form to the other under the rules of mathematical topology. Although intriguing and discussed as early as 1961, to date all methods of accessing molecules containing only this topological stereogenic element require the separation of the mirror-image forms via chiral stationary phase high-performance liquid chromatography, which has limited their investigation to date. Here, we present a simple method that uses a readily available source of chiral information to allow the stereoselective synthesis of topologically chiral catenanes.

| S-EPMC6588264 | biostudies-literature

Enantioselective radical conjugate additions driven by a photoactive intramolecular iminium-ion-based EDA complex.

Project description:The photochemical activity of electron donor-acceptor (EDA) complexes provides a way to generate radicals under mild conditions. This strategy has found application in chemical synthesis and recently in enantioselective catalysis. Reported methods classically relied on the formation of intermolecular EDA complexes, generated upon aggregation of two suitable reagents. Herein, we further expand the synthetic utility of this strategy demonstrating that an intramolecular EDA complex can trigger a photochemical catalytic enantioselective radical process. This approach enables radical conjugate additions to β-substituted cyclic enones to form quaternary carbon stereocenters with high stereocontrol using visible light irradiation. Crucial for success is the use of an amine catalyst, adorned with a carbazole moiety, which generates, upon condensation with enones, chiral iminium ions that show a broad absorption band in the visible region. This optical property originates from an intramolecular charge transfer π-π interaction between the electron-rich carbazole nucleus and the electron-deficient iminium double bond.

| S-EPMC6095928 | biostudies-literature

Stereoselective synthesis of perillaldehyde-based chiral ?-amino acid derivatives through conjugate addition of lithium amides.

Project description:The Michael addition of dibenzylamine to (+)-tert-butyl perillate (3) and to (+)-tert-butyl phellandrate (6), derived from (S)-(-)-perillaldehyde (1), resulted in diastereomeric ?-amino esters 7A-D in a moderately stereospecific reaction in a ratio of 76:17:6:1. After separation of the diastereoisomers, the major product, cis isomer 7A, was quantitatively isomerized to the minor component, trans-amino ester 7D. All four isomers were transformed to the corresponding ?-amino acids 10A-D, which are promising building blocks for the synthesis of ?-peptides and 1,3-heterocycles in three steps. The steric effects of the isopropyl group at position 4 and of the ?-methyl substituent of (R)-N-benzyl-N-?-methylbenzylamine on the reactivity were also studied and, upon application of a chiral amine, excellent stereoselectivity of the conjugate addition was observed. Amino ester 11 was obtained as a single product and transformed to the corresponding amino acids 10A and 10D in good yields on the gram scale.

| S-EPMC4273274 | biostudies-literature

Stereoselective access to tubuphenylalanine and tubuvaline: improved Mn-mediated radical additions and assembly of a tubulysin tetrapeptide analog.

Project description:Synthesis of tubuphenylalanine and tubuvaline (Tuv), α-substituted γ-amino acid building blocks for tubulysin family of antimitotic compounds, has been improved using a radical addition reaction in the presence of unprotected hydroxyl functionality. The key carbon-carbon bond construction entails stereoselective Mn-mediated photolytic additions of alkyl iodides to the C=N bond of chiral N-acylhydrazones, and generates the chiral amines in high yield with complete stereocontrol. Reductive N-N bond cleavage and alcohol oxidation converted these amino alcohols into the corresponding γ-amino acids. The route to Tuv proceeded via peptide coupling with serine methyl ester, followed by a high-yielding sequence to convert the serine amide to a thiazole. Finally, peptide bond construction established the tubulysin framework in the form of a C-terminal alcohol analog. Attempted oxidation to the C-terminal carboxylate was unsuccessful; control experiments with dipeptide 18 showed a cyclization interfered with the desired oxidation process.

| S-EPMC4924578 | biostudies-literature

Enantioselective conjugate silyl additions to cyclic and acyclic unsaturated carbonyls catalyzed by Cu complexes of chiral N-heterocyclic carbenes.

Project description:An efficient Cu-catalyzed protocol for enantioselective addition of a dimethylphenylsilanyl group to a wide range of cyclic and acyclic unsaturated ketones, esters, acrylonitriles, and alpha,beta,gamma,delta-dienones is disclosed. Reactions are performed in the presence of 1-2 mol % of commercially available and inexpensive CuCl, a readily accessible monodentate imidazolinium salt, and commercially available (dimethylphenylsilyl)pinacolatoboron. Cu-catalyzed enantioselective conjugate additions proceed to completion within only 2 h to afford the desired silanes in 87-97% yield and 90:10-99:1 enantiomeric ratio (er). Use of a proton source (e.g., MeOH) is not required; accordingly, synthetically versatile alpha-silyl boron enolates can be obtained. The special utility of the present protocol, in comparison with the related catalytic enantioselective aldol and boronate conjugate additions, is discussed and illustrated through various functionalizations of the enantiomerically enriched beta-silylcarbonyls.

| S-EPMC2836128 | biostudies-literature

Second-generation DBFOX ligands for the synthesis of beta-substituted alpha-amino acids via enantioselective radical conjugate additions.

Project description:A set of second-generation DBFOX ligands possessing extended aryl or benzyl-type groups was synthesized. The requisite amino alcohols were either commercially available (DBFOX/Bn) or constructed via Sharpless asymmetric aminohydroxylation (DBFOX/Nap, DBFOX/ t-BuPh, DBFOX/Pip) or phase-transfer-catalyzed asymmetric alkylation (DBFOX/MeNap). Complexes of the ligands with Mg(NTf2)2 were evaluated as promoters of enantioselective radical conjugate additions to alpha,beta-unsaturated alpha-nitro amides and esters. Reactions employing the DBFOX/Nap ligand exhibited improved enantioselectivity relative to previously published additions mediated by DBFOX/Ph. However, the relatively modest increase in diastereomeric ratio suggests that our substrate-Lewis acid binding model, which was formulated based on results from DBFOX/Ph-promoted radical conjugate additions, is in need of revision.

| S-EPMC2627584 | biostudies-literature

Stereoselective additions of thiyl radicals to terminal ynamides.

Project description:Two complementary sets of conditions for radical additions of thiols to terminal ynamides are described. The use of 1 equiv of thiol affords the cis-beta-thioenamide adducts in rapid fashion (10 min) and good dr, whereas employing excess thiol and longer reaction times favors the trans products.

| S-EPMC2878391 | biostudies-literature