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Topic: Another interesting transformation  (Read 7090 times)

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Offline Dan

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Another interesting transformation
« on: November 26, 2009, 04:17:33 AM »
As Heory requested, I'm going to post an interesting transformation that came up in group problems this week.

Propose mechanisms for the following transformations, and predict the final product's structure.
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Offline jinclean

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Re: Another interesting transformation
« Reply #1 on: November 26, 2009, 05:17:46 AM »
Oh!My god...  i get mad of it.too many steps!!!and what is the RuCl3 for?
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Offline Heory

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Re: Another interesting transformation
« Reply #2 on: November 26, 2009, 09:03:47 AM »
 ???
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Offline Dan

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Re: Another interesting transformation
« Reply #3 on: November 26, 2009, 09:41:23 AM »
That's close! Can you give intermediates/mechanisms and we can see where you went wrong.
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Offline Heory

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Re: Another interesting transformation
« Reply #4 on: November 26, 2009, 10:42:54 AM »
 :)
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Offline Dan

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Re: Another interesting transformation
« Reply #5 on: November 26, 2009, 11:04:23 AM »
Ok, you made the same mistake I did when I first saw step (i). You went too far - remember we're at low temperature...

Also, step 4 is more than just a work up...
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Offline Heory

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Re: Another interesting transformation
« Reply #6 on: November 26, 2009, 12:05:21 PM »
Sorry for the ugly picture, for i'm too tired and must go to bed. how about this?
PS:Dan, you are a great indicator.
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Offline Dan

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Re: Another interesting transformation
« Reply #7 on: November 26, 2009, 12:36:55 PM »
Yup, good work!

This is a rather lengthy dehydration strategy. Selective activation of the primary hydroxyl led to rapid furan formation - the [3.2.1] bicyclic system - the observation that this displacement occurred readily led to the clever bridging strategy - [4.3.1] bicyclic system - with SOCl2, which is then activated as a better leaving group by oxidation in step (ii).

Selenide displacement at the less hindered alkyl sulfate followed by hydrolysis allowed elimination via the selenoxide - 67% over 5 steps.

Ref:

Kuniaki Tatsuta, Satoshi Nakano, Fumie Narazaki, Yusuke Nakamura Tetrahedron Letters 2001, 42, 7625-7628.
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Offline tmartin

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Re: Another interesting transformation
« Reply #8 on: November 27, 2009, 09:36:43 AM »
Quite an interesting reaction sequence!  I don't think I've ever seen SOCl2 used that way, but after seeing it laid out it makes sense.
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