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Topic: bormination  (Read 3276 times)

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Offline GinaTageldin

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bormination
« on: January 24, 2016, 11:15:42 AM »
Dear members
i had a question in a reaction while i was going to brominate active methyl group to give CH2Br since it was present between 2 Nitrogen atoms ,the nmr elucidated that the phenyl ring was brominated at the para position , the reaction was performed by adding bromine in galcical acetic to the compund already dissolved in bromine ???
how to prove that bromination underwent easily and in absence of lewis base
thank you for your help

Offline TheUnassuming

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Re: bormination
« Reply #1 on: January 24, 2016, 01:05:48 PM »
Not sure I'm understanding you correctly.  You tried to brominate a methyl that is alpha to a carbonyl to form the alpha bromoketone? 
When in doubt, avoid the Stille coupling.

Offline GinaTageldin

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Re: bormination
« Reply #2 on: January 24, 2016, 02:29:09 PM »
this structure similary have the same idea while bromination of the CH3 gp the phenyl ring become brominated not CH3

Offline AWK

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Re: bormination
« Reply #3 on: January 24, 2016, 03:22:48 PM »
Aromatics are brominated through electrophilic aromatic substitution mechanism, aliphatics through a completely different radical mechanism.
AWK

Offline TheUnassuming

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Re: bormination
« Reply #4 on: January 24, 2016, 03:46:22 PM »
Are you following a lit prep for a similar substrate?
When in doubt, avoid the Stille coupling.

Offline GinaTageldin

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Re: bormination
« Reply #5 on: January 25, 2016, 10:12:17 AM »
yes literature dercribed two procedures 1st Br2 Acetic
2nd n bromosuccinimide in presence of benzoyl peroxide in THF
but the procedure used was the 1st which indication of bromination of phenyl ring not CH3 how to explain the mechanism???/

Offline TheUnassuming

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Re: bormination
« Reply #6 on: January 26, 2016, 08:36:29 AM »
The phenyl ring must be more activated than your desired bromination position.  There are some selectivity differences between NBS and Br2, so give the other a try and see if you get the results you want.
When in doubt, avoid the Stille coupling.

Offline clarkstill

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Re: bormination
« Reply #7 on: January 26, 2016, 09:07:42 AM »
Did you say bromine was added to the compound dissolved in bromine?!? Nasty...

Offline GinaTageldin

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Re: bormination
« Reply #8 on: January 29, 2016, 02:28:09 PM »
no i dissolve the compound in acetic acid

Offline GinaTageldin

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Re: bormination
« Reply #9 on: January 29, 2016, 02:31:52 PM »
my question is is that possible to brominate the phenyl ring in absence of lewis acid and if yes what is the mechanism

Offline TheUnassuming

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Re: bormination
« Reply #10 on: January 29, 2016, 02:46:42 PM »
Yes, it is possible.  This sort of reaction (without a metal catalyst) is not uncommon and only requires a sufficiently activated ring system.  How do you add a halogen to an aromatic ring typically?
When in doubt, avoid the Stille coupling.

Offline GinaTageldin

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Re: bormination
« Reply #11 on: January 30, 2016, 03:16:08 AM »
thank you so much

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