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Ring-Closing Metathesis in Methanol and Water

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journal contribution
posted on 01.12.1998, 00:00 by Thomas A. Kirkland, David M. Lynn, Robert H. Grubbs
The ring-closing metathesis (RCM) of acyclic dienes in both methanol and water has been achieved through the use of water-soluble ruthenium alkylidenes. These alkylidenes react readily with acyclic olefins in protic solvents, but they do not cyclize α,ω-dienes because of the instability of the resulting methylidene. Successful cyclization has been achieved through simple substrate modificationincorporation of an olefin substituent allows cyclization to proceed in good yield. A methyl-substituted substrate was cyclized in 60% conversion in methanol, and the incorporation of a phenyl substituent resulted in nearly quantitative cyclization. Phenyl-substituted substrates are best suited for the reaction, as a more stable, active catalyst is regenerated upon each catalyst turnover. Using this methodology, 90% conversion of a water-soluble substrate to a substituted cyclopentene has been achieved in aqueous solution. This methodology has also been successfully applied to increase RCM yields in organic solvents.