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An Easier Way To Go From E To Z

Olefin Isomerization: Chemists borrow the vision vitamin riboflavin to use as a photocatalyst to synthesize hard-to-make Z olefins

by Stephen K. Ritter
September 14, 2015 | A version of this story appeared in Volume 93, Issue 36

Taking inspiration from the light-driven double-bond isomerization of retinal in the eyes that helps control our vision, chemists in Germany have created a generic catalytic synthetic process for converting activated E olefins to Z olefins (J. Am. Chem. Soc. 2015, DOI: 10.1021/jacs.5b07136). Z olefins are structurally cramped molecules that are usually less stable than their E isomers, making them hard to synthesize—they tend to isomerize back to the E olefin. Jan B. Metternich and Ryan Gilmour of the University of Münster, in Germany, were looking for a better way to make Z olefins when they found a reference noting that riboflavin (vitamin B-2) can serve as a chromophore to activate (E)-retinal and help isomerize it to (Z)-retinal. Using the retinal isomerization as a model, the researchers designed a riboflavin-catalyzed reaction for selectively converting planar, conjugated E olefins to twisted, deconjugated Z olefins. The twisted Z olefins they made are inefficiently excited by light, so they can’t revert to their E isomer. The trick is using shorter olefins with one double bond, rather than a polyene such as retinal, and adding another substituent to the chain to further increase unfavorable nonbonding interactions after isomerization. The Münster team says this approach should be useful in organic synthesis to make complex molecular scaffolds for drug discovery and agrochemical research.


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