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Topic: Practice problem 4  (Read 5173 times)

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Offline SinkingTako

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Practice problem 4
« on: April 24, 2014, 09:51:49 AM »
See attached, and propose a mechanism. Hint: it involves a Claisen rearrangement.
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Offline Rutherford

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Re: Practice problem 4
« Reply #1 on: April 24, 2014, 11:36:06 AM »
This:

Offline SinkingTako

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Re: Practice problem 4
« Reply #2 on: April 24, 2014, 11:49:26 AM »
Hmm, close, but looks slightly weird. How did you form your R-OTs in the first step from the alcohol? (I mean is it favoured over other reactions with an acid?) I think the rearrangement shouldn't have involved the Ts.
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Offline SinkingTako

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Re: Practice problem 4
« Reply #3 on: April 24, 2014, 11:56:45 AM »
And on a side note TsOH, MsOH, TfOH should all be non-nucleophilic.
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Offline Rutherford

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Re: Practice problem 4
« Reply #4 on: April 24, 2014, 12:34:23 PM »
Oh I've mistaken TsOH for TsCl.

Offline Rutherford

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Re: Practice problem 4
« Reply #5 on: April 26, 2014, 12:32:07 PM »
If no one answers soon, you could give an additional hint.

Offline SinkingTako

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Re: Practice problem 4
« Reply #6 on: April 26, 2014, 12:53:56 PM »
Okay, see below for the first step. After this should be the formation of a regular claisen enol-ether.
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Offline Rutherford

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Re: Practice problem 4
« Reply #7 on: April 30, 2014, 12:06:22 PM »
Okay, OH group gets protonated and eliminated. Then this rearrangement happens:
Right?

Offline SinkingTako

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Re: Practice problem 4
« Reply #8 on: April 30, 2014, 12:52:18 PM »
Yeap yeap yeap! This is correct! *clap clap* Your turn to post a question!

But I think it is slightly more correct to draw the arrow going in the other direction (ie anti-clockwise instead of clockwise), because usually it's the alpha carbon that is nucleophilic. Though since it's pericyclic doesn't actually matter that much.

Sigh I really hope that this problem thing can last. People lurking in this forum respond please?
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Offline Rutherford

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Re: Practice problem 4
« Reply #9 on: April 30, 2014, 01:23:55 PM »
After your hint it was pretty obvious (you even said that it is Claisen afterwards). I waited for someone else to answer, but nothing.

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