Selected substituent effects on the rate and efficiency of formation of an eight-membered ring by RCM

L. Mitchell, J.A. Parkinson, Jonathan Percy, K. Singh

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Abstract

Studies of a range of reactions forming cyclooctenones highlight a discrepancy between cyclization rate and cyclization efficiency. Cyclization rates change modestly as the oxygen function at the allylic position is varied, and increase upon gem-dimethylation. Cyclization efficiency has also been quantified for four substrates, revealing a range of effective molarities (EMs) of 2 orders of magnitude that are substituent dependent. The most efficient cyclization appears to result from suppression of the cross-metathesis pathway through which oligomerization begins, rather than from a particularly rapid cyclization reaction. In the presence of a Ti(IV) cocatalyst, diene monomers transform smoothly to eight-membered-ring products without the intermediacy of dimers or other oligomers, indicating that the cyclizations are kinetically and not thermodynamically controlled. The gem-dialkyl effect is also shown to be kinetic.
Original languageEnglish
Pages (from-to)2389-2395
Number of pages7
JournalJournal of Organic Chemistry
Volume73
Issue number6
DOIs
Publication statusPublished - 21 Mar 2008

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Keywords

  • cyclization
  • cyclooctenones
  • substituent effects
  • effective molarities
  • RCM

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