Douglas B. Grotjahn, Casey R. Larsen, Jeffery L. Gustafson, Reji Nair, and Abhinandini Sharma: JACS 2007, DOI: 10.1021/ja073457i
Monday, July 23, 2007
An Alkene Zipper Reaction
Aaron over at Carbon Based Curiosities has recently posted about one of my favorite reactions, the alkene zipper reaction catalyzed by 1,3-diaminopropane and potassium hydride. Most of the time this reaction works great, but it is thermodynamic and has some problems when your alkyne is stabilized by conjugation. Anyway, an interesting paper appeared on the JACS ASAP web site last week dealing with the alkene version of a zipper reaction. It is a very nice contribution from Doug Grotjahn and co-workers from San Diego State University. It utilizes a bifunctional ruthenium catalyst to walk an alkene down the chain until it reaches an alcohol. Once an enol is generated it quickly tautomerizes to the ketone form thus providing the thermodynamic sink for the reaction to fall into. The imidazole ligand on the catalyst was crucial for success and may be involved in the isomerization. A very interesting example of this difficult to accomplish process.
Douglas B. Grotjahn, Casey R. Larsen, Jeffery L. Gustafson, Reji Nair, and Abhinandini Sharma: JACS 2007, DOI: 10.1021/ja073457i
Douglas B. Grotjahn, Casey R. Larsen, Jeffery L. Gustafson, Reji Nair, and Abhinandini Sharma: JACS 2007, DOI: 10.1021/ja073457i
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8 comments:
Anything known about the mechanism?
who is this "aaron" fellow you speak of?
shutup, you aaron
kutti:
The paper suggests that the double bond complexes with Ru and nitrogen strips off an adjacent proton, creating an allylic Ru ligand. The proton is picked up by the opposite side of the allylic system, and Ru continues on its merry way.
How do you know that the ruthenium doesn't just oxidize the alcohol, and the resulting hydride then reduces the double bond? I don't think the key control experiment has been done to rule out this potential mechanism? That has been observed previously.
in response to the last comment posted, the ruthenium does not oxidize the alkenol to the aldehyde. if you look at the other substrates, the isomerization occurs. its rather amazing data....with more to come...
could also essentially be a transfer dehydrogenation between two molecules of substrate. i'd look for traces of ketone w/alkene present. during the course of the reaction there should also be alcohol with internal alkene, which i don't think is mentioned in the paper. ultimately, a mixed isotopic labeling study which shows a D staying on (or not moving to) a substrate which is 13C or 18O labeled would be the best evidence that this is truly isomerizing down the same chain.
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