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Topic: Problem of the Week - 10/26/09  (Read 18762 times)

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Offline Heory

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Re: Problem of the Week - 10/26/09
« Reply #15 on: October 29, 2009, 03:50:14 PM »
the diene nucleophile is just like that in Prinse reaction, but here it may be a side reaction. if the answer was as simple as the acetal, i would be crazy ???

Offline azmanam

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Re: Problem of the Week - 10/26/09
« Reply #16 on: October 29, 2009, 04:30:47 PM »
couldn't sleep? :)

haha.  all that functionality just for an acetal formation?  that would be an awesome trick question.  The acetal is the initial product of the diol/aldehyde/L.A.  Once formed, the diol will continue to react.  We're on the right track now.
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Offline nj_bartel

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Re: Problem of the Week - 10/26/09
« Reply #17 on: October 29, 2009, 08:48:16 PM »
The acetal formation in this case is allowed to proceed to an appreciable extent due to the carbonyl oxygen coordination to the boron complex, yes?

Offline azmanam

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Re: Problem of the Week - 10/26/09
« Reply #18 on: October 29, 2009, 08:50:05 PM »
yup, lewis acid activation lowers the activation energy for addition to oxonium ions.  loss of water gets us to the acetal
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Offline Heory

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Re: Problem of the Week - 10/26/09
« Reply #19 on: October 30, 2009, 12:23:04 AM »
another guess:

Offline nj_bartel

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Re: Problem of the Week - 10/26/09
« Reply #20 on: October 30, 2009, 12:56:20 AM »
What's the leaving group in that last step?

O+-B--F3?

Offline Heory

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Re: Problem of the Week - 10/26/09
« Reply #21 on: October 30, 2009, 01:00:58 AM »
something was wrong and i'll think of it for some time

Offline Heory

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Re: Problem of the Week - 10/26/09
« Reply #22 on: October 30, 2009, 01:10:06 AM »
q

Offline azmanam

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Re: Problem of the Week - 10/26/09
« Reply #23 on: October 30, 2009, 07:36:53 AM »
nope :). my hint for the second step of the mechanism: remember that acetals are in equilibrium
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Offline Heory

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Re: Problem of the Week - 10/26/09
« Reply #24 on: October 30, 2009, 08:33:25 AM »
It's quite a difficult work to predict the product, because many paths exist for the reaction. If this is still not right, I'd like you to tell me more information about it.

Offline azmanam

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Re: Problem of the Week - 10/26/09
« Reply #25 on: October 30, 2009, 11:07:38 AM »
you've got the right transformation (which named reaction is this?), but the wrong regiochemistry.  why did you choose that c-c bond to make?
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Offline Dan

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Re: Problem of the Week - 10/26/09
« Reply #26 on: October 30, 2009, 01:28:23 PM »
Hmmm. Good work on the acetal Heory!

Something like this?

This terpene stuff is making me itch for a hydride shift... but I can't see a good oppertunity.
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Offline azmanam

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Re: Problem of the Week - 10/26/09
« Reply #27 on: October 30, 2009, 01:51:39 PM »
that's the right C-C bond formation.  The orientation of the alkene-containing side chain will be dictated by steric clash with the isopropyl group... but the diene-containing 6-membered ring will not adopt a chair conformation, so we'll need to rethink the origin of selectivity in the c-c bond forming step (still need a name for this reaction).

The chemistry after the c-c bond forming step is not correct yet.  different things happening here.  getting closer :)
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Offline Heory

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Re: Problem of the Week - 10/26/09
« Reply #28 on: October 30, 2009, 05:57:59 PM »
 :)

Offline azmanam

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Re: Problem of the Week - 10/26/09
« Reply #29 on: October 31, 2009, 09:49:52 AM »
you're correct up to your last step.  Still looking for a name for the c-c bond forming step (and there will be a name for the final step).  you've got the right idea, but hydride doesn't transfer.  I think as a result of geometry, but I might have to look at a model.  anyway, we're quite close now.
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