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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: zsinger on April 22, 2014, 07:35:39 PM

Title: Skattebol Rearrangement Question
Post by: zsinger on April 22, 2014, 07:35:39 PM
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
Title: Re: Skattebol Rearrangement Question
Post by: AlphaScent on April 23, 2014, 09:55:59 AM
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?
Title: Re: Skattebol Rearrangement Question
Post by: Archer on April 23, 2014, 12:01:34 PM
Can you attach the mechanism you are talking about? or at least provide the starting gem-dihalide?
Title: Re: Skattebol Rearrangement Question
Post by: AlphaScent on April 23, 2014, 03:45:43 PM
This is what I see for a general mechanism.  Zack, are you talking about cyclooctane-cyclopropane bicyclo system?
Title: Re: Skattebol Rearrangement Question
Post by: zsinger on April 23, 2014, 04:09:38 PM
Precisely!
Title: Re: Skattebol Rearrangement Question
Post by: AlphaScent on April 23, 2014, 04:25:15 PM
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. 

Title: Re: Skattebol Rearrangement Question
Post by: Archer on April 23, 2014, 04:52:37 PM
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.

C1CC=C=C(C2=CC=CC=C2)CCCC1