Ring-closing metathesis in methanol and water

The ring-closing metathesis (RCM) of acyclic dienes in both methanol and wa ter has been achieved through the use of water-soluble ruthenium alkylidene s. These alkylidenes react readily with acyclic olefins in protic solvents, but they do not cyclize alpha,omega-dienes because of the instability of t he 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 c yclized in 60% conversion in methanol, and the incorporation of a phenyl su bstituent resulted in nearly quantitative cyclization. Phenyl-substituted s ubstrates are best suited for the reaction, as a more stable, active cataly st is regenerated upon each catalyst turnover. Using this methodology, 90% conversion of a water-soluble substrate to a substituted cyclopentene has b een achieved in aqueous solution. This methodology has also been successful ly applied to increase RCM yields in organic solvents.