Reversal Of Diastereoselectivity Research Articles

Diastereocontrol in Lewis acid-catalyzed Michael reactions of 4-siloxycyclopentenone with ketene silyl acetals: Stereoelectronic vs. steric effect

The title reactions are shown to proceed with sterically unfavorable syn preference (to the siloxy group) when steric demand of the acetals is trivial, whereas β-substitution of acetals results in reversal of diastereoselection. These results are discussed in terms of the stereoelectronic vs. steric effect.

Preparation of both enantiomers of an α-hydroxy ketone via biocatalytic reduction and chemical oxidation

2-Hydroxy-2,6,6-trimethylcyclohexanone 1 is a key intermediate for the synthesis of naturally occurring bioactive metabolites, viz. 2A-B and 3. Both enantiomers of this key intermediate 1 were obtained by sterospecific reduction using Bakers' yeast under nonfermenting conditions followed by chemical oxidation. Free as well as immobilized cells were tested in aqueous and organic media for their ability to catalyze the sterospecific reduction of the parent ketone 1. Preparative scale biotransformation of 1 in aqueous medium using free cells of Bakers' yeast produced two diastereomeric alcohols 4 and 5 at a ratio of approximately 1 :4 and 9.1% and 36.4% chemical yields, respectively. The reduced products exhibited high enantiomeric excess (>90%) as analyzed by 1H and 13C-NMR spectroscopy. Unreduced hydroxy ketone was found to be highly enriched in S (−)- 1, while chemical oxidation of the diol 5 gave R (+) 1. A reversal of diastereoselectivity was observed when an organic medium was used for biotransformation.

ChemInform Abstract: Reversal of Diastereoselectivity in the Addition of C‐Nucleophiles to N‐Trimethylsilyl Imines via Grignard Derived Organo Copper‐Boron Trifluoride Reagents.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reversal of diastereoselectivity in the addition of C-nucleophiles to N-trimethylsilyl imines via Grignard derived organo copper-boron trifluoride reagents.

The N-trimethylsilyl imines of O-protected α-hydroxy aldehydes react with RCuMgXI BF 3 to give β-amino alcohols with high anti diastereoselectivity.

ChemInform Abstract: Highly Diastereoselective Reactions of Ytterbium‐Mediated Alkynyllithium and Alkynylmagnesium Reagents with Chiral 2‐Acyl‐1,3‐ oxathianes: Reversal of Diastereoselectivity.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reversal of diastereoselectivity in protonation of chiral photodienols

The configuration of the new asymmetric center created in the photodeconjugation of an α-substituted α,β-unsaturated ester derived from exo, exo-benzyloxybornanol depends on the structure of the achiral species used as the catalyst of the protonation of the intermediate dienol. Thus, the ratio of the deconjugated diastereoisomers varies from 91 9 to 37 63 .

Reversal of Diastereoselectivity in Reactions of Acyclic and Cyclic Radicals

Reversal of Diastereoselectivity in Reactions of Acyclic and Cyclic Radicals

Stereoselective synthesis of alcohols, XXXIV. Towards an understanding of cram/anti‐cram selectivity on addition of crotylboronates to α‐methylbutyraldehyde

AbstractThe diastereoselectivity on addition of γ‐substituted allylboronates to α‐methylbutyraldehyde (9) did not depend on the size of the substitutent in the reagent, but only on its location in the Z or E position. This finding required a reinterpretation of the reasons for the attendant reversal in diastereoselectivity. New hypotheses are presented based on force‐field calculations on model structures for the transition states.

Highly diastereoselective reactions of ytterbium-mediated alkynyllithium and alkynylmagnesium reagents with chiral 2-acyl-1,3-oxathianes: reversal of diastereoselectivity

Highly diastereoselective reactions of ytterbium-mediated alkynyllithium and alkynylmagnesium reagents with chiral 2-acyl-1,3-oxathianes: reversal of diastereoselectivity

Concerning reversal of diastereoselectivity in the BF 3 promoted addition of crotyl—organometallic compounds to aldehydes

The addition of a mixture of benzaldehyde and BF 3·OEt 2 to crotyl-organometallic reagents C 4H 7MLn ( 1) (M = Cu, Cd, Hg, Tl, Ti, Zr and V) produces predominantly the erythro homoallyl alcohol as well as the α-adduct, while without BF 3·OEt 2 the threo isomer is formed preferentially.

Reversal of diastereoselectivity in the BF3-promoted addition of halobis(cyclopentadienyl)crotyltitanium compounds to aldehydes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTReversal of diastereoselectivity in the BF3-promoted addition of halobis(cyclopentadienyl)crotyltitanium compounds to aldehydesM. T. Reetz and M. SauerwaldCite this: J. Org. Chem. 1984, 49, 12, 2292–2293Publication Date (Print):June 1, 1984Publication History Published online1 May 2002Published inissue 1 June 1984https://doi.org/10.1021/jo00186a045RIGHTS & PERMISSIONSArticle Views128Altmetric-Citations38LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (285 KB) Get e-Alerts Get e-Alerts