Issue Date: December 19, 2011
Catching Z Olefins
Scientists who had been losing sleep over the metathesis reaction’s preference to form E olefins were finally able to catch some Zs this year—Z olefins, that is. Using a new molybdenum catalyst, Boston College’s Amir H. Hoveyda, MIT’s Richard R. Schrock, and coworkers figured out a way to rig cross-metathesis reactions to preferentially produce the less stable, structurally cramped isomer with Z double bonds (C&EN, March 28, page 9; Nature, DOI: 10.1038/nature09957). Researchers led by Caltech’s Robert H. Grubbs were similarly able to selectively form Z olefins, but by using new ruthenium catalysts (C&EN, May 23, page 33; J. Am. Chem. Soc., DOI: 10.1021/ja202818v and 10.1021/ja210225e). In olefin metathesis chemistry, two carbon-carbon double bonds react to form a new alkene and an alkene by-product, usually ethylene. Through careful catalyst design, both groups were able to shift products toward the Z isomers. Grubbs and coworkers demonstrated the utility of the ruthenium catalysts by using them to make a pheromone-like molecule that is industrially relevant in insect pest control. Hoveyda and Schrock’s team used its molybdenum catalyst en route to preparing the immunostimulant KRN7000 and an antioxidant plasmalogen phospholipid. Expanding on their efforts to make Z olefins, Hoveyda and Schrock, working in collaboration with the University of Oxford’s Darren J. Dixon, also reported a tungsten catalyst that selectively forms Z alkenes in ring-closing metathesis reactions (C&EN, Nov. 7, page 11; Nature, DOI: 10.1038/nature10563). The researchers used the tungsten catalyst to stereoselectively synthesize the anticancer compound epothilone C and the antimicrobial compound nakadomarin A.
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