September 23, 2021, 02:40:05 AM
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Topic: Would love some help on this cyclization mechanism (pyrrole synthesis final step  (Read 2369 times)

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Offline janapix

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I'm having a hard time figuring out the reaction mechanism for this one, as well as why alternative cyclization products aren't formed.
Do YOU know?


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Offline Guitarmaniac86

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The Paal Knorr synthesis proceeds via an imine. I think your first structure is wrong.

With the imine, it is in equilibrium with the enamine form, of which the lone pair on the nitrogen will attack the carbonyl carbon of the methyl ketone portion of the molecule to complete the ring closing.

Change the structure of the starting compound and it should be clearer.
Don't believe atoms, they make up everything!

Offline janapix

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First of all, thanks for the reply.
I've made the change you recommended and was wondering... does this look right to you?
-fingers crossed-


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Offline Guitarmaniac86

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I was thinking something more like the following. I have omitted a lot of steps in the mechanism, but here is some of it.



The three membered rings in your mechanism are too unstable to form.

Also, in your second to last step when the oxygen -ve charge electrons fall back in, they will eliminate OEt because it is a very good leaving group so you wouldnt get your product. Think what product will actually form in this instance, if this was the case.

Hope this helps a little.
Don't believe atoms, they make up everything!

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