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Topic: cope elimination  (Read 9385 times)

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Offline ksr985

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cope elimination
« on: May 14, 2005, 05:10:22 PM »
I have a tertiary amine, dimethyl s-butyl amine. I react it with MCPBA, in THF and then heat. Comment on the stereochemistry of the product.

i think its the Cope reaction, but will it give the cis or trans alkene?
« Last Edit: May 16, 2005, 04:17:30 AM by ksr985 »
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Offline Donaldson Tan

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Re:weird amine
« Reply #1 on: May 14, 2005, 05:16:29 PM »
if the chiral carbon contains 2 methyl group, how can it be an enantiomer?
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

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Re:weird amine
« Reply #2 on: May 14, 2005, 08:15:18 PM »
never thinked about it, but i know that Chugaev Reaction (Tschugaeff Olefin Synthesis) generate only cis olefinic products, so i suppose that you should obtain only cis olefins also with the cope elimination.

In addition i found this:
Mechanistic study: R. D. Bach, M. L. Braden, J. Org. Chem. 56, 7194 (1991)

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Re:weird amine
« Reply #3 on: May 15, 2005, 02:48:51 PM »
This isn't a Cope reaction of a Chugaev reaction.  It's just an oxidation of the amine to the N-oxide.

Cope:
http://www.organic-chemistry.org/frames.htm?http://www.organic-chemistry.org/namedreactions/cope-rearrangement.shtm

Chugaev:
http://themerckindex.cambridgesoft.com/TheMerckIndex/NameReactions/onr74.htm

The alkyl groups are all on the nitrogen, right?  If so, then there is one stereocenter in the N-oxide product.  This N-oxide might undergo another reaction though, but I can't think of what it would be.


Offline ksr985

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Re:weird amine
« Reply #4 on: May 15, 2005, 03:06:16 PM »
i am pretty sure its a cope reaction. not cope rearrangement. cope elimination.
i just dont know if the final product is cis or trans.
all three groups are attached to nitrogen
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Re:weird amine
« Reply #5 on: May 15, 2005, 07:09:03 PM »
Ah, I see.

Cope elimination reaction:
http://themerckindex.cambridgesoft.com/TheMerckIndex/NameReactions/onr82.htm

I would approach the problem in this way:  Think about what the transition state of the transformation will look like.  You should find that there are two similar reaction pathways that lead to two stereochemically different products.  Which transition stat would you figure to be the lower in energy and why?

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Offline ksr985

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Re:weird amine
« Reply #7 on: May 16, 2005, 03:34:29 AM »
aha! thanks. so, essentially it is an internal syn elimination.
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Re:cope elimination
« Reply #8 on: May 16, 2005, 01:36:15 PM »
Essentially, yes.  I would think of it more as an electrocyclic process though.

Did you figure out what the stereodetermining interaction would be?  There should be two possibilities for the elimination.

Offline ksr985

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Re:cope elimination
« Reply #9 on: May 16, 2005, 03:11:01 PM »
The stereodetermining factor should be the orientation of the groups on the beta carbon. The  H being removed and the O have to be 'syn' with respect to each other.. if one draws the sawhorse projection of the initial amine oxide, it becomes relatively easy to determine whether the product will be E or Z, keeping the H and N almost eclipsed. Am i more or less correct, movies?

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Re:cope elimination
« Reply #10 on: May 16, 2005, 03:45:27 PM »
I think we're on the same page, but I'm not entirely certain.

Which product do you predict? (E or Z)

Offline ksr985

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Re:cope elimination
« Reply #11 on: May 17, 2005, 04:17:00 AM »
i dont think its possible to say which isomer will be formed, in this particular example. This is because, there are two hydrogens that can be removed from the beta carbon, and two diastereomeric products can be obtained from their  elimination.E and Z. hm?
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Re:cope elimination
« Reply #12 on: May 17, 2005, 12:59:17 PM »
i dont think its possible to say which isomer will be formed, in this particular example. This is because, there are two hydrogens that can be removed from the beta carbon, and two diastereomeric products can be obtained from their  elimination.E and Z. hm?

This is true, but I think that you can predict which one will be favored.  Try building a model of the N-oxide intermediate and look at the two transtion states.

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