Different Metal, Different Isomer | November 17, 2008 Issue - Vol. 86 Issue 46 | Chemical & Engineering News
Volume 86 Issue 46 | p. 55 | Concentrates
Issue Date: November 17, 2008

Different Metal, Different Isomer

Simply choosing a ruthenium or a palladium catalyst provides a novel means of diastereocontrol when making complex bicyclic compounds
Department: Science & Technology
News Channels: JACS In C&EN

Exquisite control over the stereoselective synthesis of bicyclic compounds is possible simply by choosing one catalyst metal over another, report Barry M. Trost, Eric M. Ferreira, and Alicia C. Gutierrez of Stanford University (J. Am. Chem. Soc., DOI: 10.1021/ja8078835). Trost's group introduced the metal-catalyzed enyne cycloisomerization reaction in 1985 as a strategy for synthesizing complex organic molecules. Follow-up studies have expanded the scope of the reaction and provided insight into the mechanism. In the latest rendition of the reaction, Trost and coworkers converted an alkyne-substituted cyclohexene into a bicyclic compound. The trans stereoisomer forms when a ruthenium catalyst is used, and the cis version forms when a palladium catalyst is used (shown). The difference plays out in one of the proposed intermediates: Both metals form a cyclic complex via coordination to the alkene and alkyne bonds of the substrate, but ruthenium uses the carbonyl oxygen of one methyl ester group to temporarily steady itself, whereas palladium does not. The result is that the carbonyl directs formation of the trans isomer, providing a novel means of diastereocontrol.

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