Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: zsinger on April 22, 2014, 07:35:39 PM
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All,
In the last step of the mechanism post Li-Halogen exchange, it indicates a ring expansion from 8 to 9 membered, with 2 alkenes oriented somewhat close to each other. Is this ring expanding simply because of the instability of the carbanion produced, the torsional strain of the 3 membered ring which it relieves, or a combination of both? Or something else :). Any help appreciated.
-Zack
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When you say close, do you mean allene close? right next to one another. I havent looked at this in a while, but isnt it a carbene rearranging to an allene?
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Can you attach the mechanism you are talking about? or at least provide the starting gem-dihalide?
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This is what I see for a general mechanism. Zack, are you talking about cyclooctane-cyclopropane bicyclo system?
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Precisely!
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So I guess just apply the mechanism to the ring and you should have it. I wonder how stable an nine membered cycloallene would be.
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These guys made it with a phenyl group attached using the above procedure.
http://onlinelibrary.wiley.com/doi/10.1002/jlac.199719970825/abstract
I am not sure of the significants of the phenyl group though as I don't have the full text. Possibly this inhibits spontaneous dimerisation.