Correlations between nucleophilicities and selectivities in the substitutions of tetrahydropyran acetals

Jennifer R. Krumper, Walter A. Salamant, K. A. Woerpel

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Abstract

(Chemical Equation Presented) Selectivities that deviate from S N1 stereoelectronic models in the nucleophilic substitutions of tetrahydropyran acetals were investigated. When weak nucleophiles were employed, stereoselectivities conformed to known SN1 stereoelectronic models. In contrast, stereoselectivities in the substitutions of acetals with strong nucleophiles depended on reaction conditions. Erosions in selectivities were observed when strong nucleophiles were employed in the absence of coordinating counterions. These erosions in selectivities are attributed to rates of nucleophilic additions to oxocarbenium ion intermediates that approach the diffusion limit. When triflate counterions were present, however, S N2-like pathways became accessible with strong nucleophiles. In most cases examined, the major stereoisomers formed from reactions that proceeded through SN2-like pathways were opposite to the major stereoisomers formed from the analogous reactions that proceeded through SN1 pathways.

Original languageEnglish (US)
Pages (from-to)8039-8050
Number of pages12
JournalJournal of Organic Chemistry
Volume74
Issue number21
DOIs
StatePublished - Nov 6 2009

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ASJC Scopus subject areas

  • Organic Chemistry

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