Erosion of stereochemical control with increasing nucleophilicity: O-glycosylation at the diffusion limit

Matthew G. Beaver, K. A. Woerpel

Research output: Contribution to journalArticlepeer-review

Abstract

(Chemical Equation Presented) Nucleophilic substitution reactions of 2-deoxyglycosyl donors indicated that the reactivity of the oxygen nucleophile has a significant impact on stereoselectivity. Employing ethanol as the nucleophile resulted in a 1:1 (α:β) ratio of diastereomers under SN1-like reaction conditions. Stereoselective formation of the 2-deoxy-α-O-glycoside was only observed when weaker nucleophiles, such as trifluoroethanol, were employed. The lack of stereoselectivity observed in reactions of common oxygen nucleophiles can be attributed to reaction rates of the stereochemistry-determining step that approach the diffusion limit. In this scenario, both faces of the prochiral oxocarbenium ion are subject to nucleophilic addition to afford a statistical mixture of diastereomeric products. Control experiments confirmed that all nucleophilic substitution reactions were performed under kinetic control.

Original languageEnglish (US)
Pages (from-to)1107-1118
Number of pages12
JournalJournal of Organic Chemistry
Volume75
Issue number4
DOIs
StatePublished - Feb 19 2010

ASJC Scopus subject areas

  • Organic Chemistry

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