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Topic: Uknown mechanism of bycyclo degradation  (Read 4714 times)

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Offline Rutherford

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Uknown mechanism of bycyclo degradation
« on: September 14, 2013, 01:33:36 PM »
What is the mechanism of the reaction leading from K to L?
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Offline discodermolide

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Re: Uknown mechanism of bycyclo degradation
« Reply #1 on: September 14, 2013, 01:53:12 PM »
Try looking at the Diels-Alder reaction.
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Offline Rutherford

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Re: Uknown mechanism of bycyclo degradation
« Reply #2 on: September 14, 2013, 03:37:58 PM »
I don't see a diene nor a dienophile here. What could have the rule of these here?
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Offline discodermolide

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Re: Uknown mechanism of bycyclo degradation
« Reply #3 on: September 14, 2013, 10:02:28 PM »
Compound K looks like it was derived from a Diels-Alder reaction.
What has happened on going from K to L?
The DA reaction often leads to aromatic compounds.
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Offline Rutherford

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Re: Uknown mechanism of bycyclo degradation
« Reply #4 on: September 15, 2013, 04:15:43 AM »
Yes, it was obtained by DA. Don't know what happened from K to L, that's what I am asking. It's new to me.
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Offline discodermolide

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Re: Uknown mechanism of bycyclo degradation
« Reply #5 on: September 15, 2013, 05:36:09 AM »
It eliminated ethylene. See if you can move the electrons around.
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Offline Rutherford

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Re: Uknown mechanism of bycyclo degradation
« Reply #6 on: September 15, 2013, 10:32:32 AM »
Is this a free-radical mechanism or not?
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Offline discodermolide

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Re: Uknown mechanism of bycyclo degradation
« Reply #7 on: September 15, 2013, 11:21:12 AM »
No it's a thermal process.
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Offline Rutherford

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Re: Uknown mechanism of bycyclo degradation
« Reply #8 on: September 15, 2013, 12:01:51 PM »
Thanks. This is an electrocyclic reaction, probably driven by the release of energy when the cyclobutane bridge disappears.
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Offline clarkstill

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Re: Uknown mechanism of bycyclo degradation
« Reply #9 on: September 16, 2013, 02:36:10 AM »
Just to clarify, it is a pericyclic cycloaddition, not an electrocyclic reaction...
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Offline Rutherford

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Re: Uknown mechanism of bycyclo degradation
« Reply #10 on: September 16, 2013, 06:36:07 AM »
What adds to what?
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Offline clarkstill

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Re: Uknown mechanism of bycyclo degradation
« Reply #11 on: September 16, 2013, 08:56:29 AM »
It's exactly as discodermolide drew: a thermal retro [4+2] cycloaddition, probably requiring high temperatures and driven by the entropy of the gaseous ethylene formed.
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Offline Rutherford

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Re: Uknown mechanism of bycyclo degradation
« Reply #12 on: September 16, 2013, 09:24:06 AM »
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Offline magician4

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Re: Uknown mechanism of bycyclo degradation
« Reply #13 on: September 16, 2013, 09:25:34 AM »
Quote
What adds to what?

though the general theme here is "cycloaddition", this in fact is not an addition, but an extrusion instead: ethylene will be expelled from the original molecule, hence "retro", i.e. the reversed process

look up "Retro Diels - Alder Reaction" : this is what happens


regards

Ingo
« Last Edit: September 16, 2013, 09:57:33 AM by magician4 »
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Offline Rutherford

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Re: Uknown mechanism of bycyclo degradation
« Reply #14 on: September 16, 2013, 10:09:30 AM »
Okay, thanks for the explanation.
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