Selected Substituent Effects on the Rate and Efficiency of Formation of an Eight-Membered Ring by RCM

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• 作者：Lisa Mitchell ; John A. Parkinson ; Jonathan M. Percy ; Kuldip Singh
• 刊名：Journal of Organic Chemistry
• 出版年：2008
• 出版时间：March 21, 2008
• 年：2008
• 卷：73
• 期：6
• 页码：2389 - 2395
• 全文大小：209K
• 年卷期：v.73,no.6(March 21, 2008)
• ISSN：1520-6904

文摘

Studies of a range of reactions forming cyclooctenones highlight a discrepancy between cyclization rateand cyclization efficiency. Cyclization rates change modestly as the oxygen function at the allylic positionis varied, and increase upon gem-dimethylation. Cyclization efficiency has also been quantified for foursubstrates, revealing a range of effective molarities (EMs) of 2 orders of magnitude that are substituentdependent. The most efficient cyclization appears to result from suppression of the cross-metathesispathway 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-ringproducts without the intermediacy of dimers or other oligomers, indicating that the cyclizations arekinetically and not thermodynamically controlled. The gem-dialkyl effect is also shown to be kinetic.