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Topic: BF3 etherate ring closing  (Read 3549 times)

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Offline AlphaScent

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BF3 etherate ring closing
« on: March 25, 2015, 09:07:36 PM »
So, Boron trifluoride etherate facilitates a ring closure similar to that of squalene to form a trans fused decalin system.  The final carbocation is on a tertiary carbon.  With the conditions only being BF3 etherate at -40; what facilitates the deprotonation to form the exo double bond?
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Offline TheUnassuming

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Re: BF3 etherate ring closing
« Reply #1 on: March 26, 2015, 09:08:12 AM »
As opposed to forming the endo-alkene?
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Offline AlphaScent

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Re: BF3 etherate ring closing
« Reply #2 on: March 26, 2015, 06:24:46 PM »
No I am wondering the mechanism of the deprotonation and double bond formation.  There is no base around to do it.  It does not happen during work up either because water would add the the carbocation.
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Offline TheUnassuming

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Re: BF3 etherate ring closing
« Reply #3 on: March 26, 2015, 09:24:04 PM »
Ah, that I don't know.  Important detail that seems to be hand waved in all my memories of lectures on the subject. 
All the mechanisms I've seen in my search tonight just seem to show the electrons flowing down from the C-H bond to form the new pi bond, and the proton just leaving. 
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Offline Dan

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Re: BF3 etherate ring closing
« Reply #4 on: March 28, 2015, 12:43:30 PM »
You can use an oxygen lone pair, either from another molecule of starting material, product, diethyl ether (which came from BF3·Et2O) or the solvent (depending on what the solvent is).
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Offline orgopete

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Re: BF3 etherate ring closing
« Reply #5 on: April 02, 2015, 07:18:31 PM »
Of a fluoride from the -OBF3(-)?
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