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Topic: Organic synthesis  (Read 10427 times)

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Offline Dan

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Re: Organic synthesis
« Reply #15 on: July 19, 2013, 03:30:05 AM »
There should be a strong thermodynamic bias for the alkene conjugated with the ketone.
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Offline magician4

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Re: Organic synthesis
« Reply #16 on: July 19, 2013, 04:42:47 AM »
I see... right now, so you'd reestablish the doublebond in the bridge....

I was planning to do the Beckmann-rearrangement first (i.e. with the alcohol still intact), as I thought it couldn't be done with alpha, beta unsaturated ketones

looking forward to learn your final solution / proposal


regards

Ingo
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Offline Dan

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Re: Organic synthesis
« Reply #17 on: July 19, 2013, 05:36:17 AM »
Quote from: magician4 on July 19, 2013, 04:42:47 AM
I was planning to do the Beckmann-rearrangement first (i.e. with the alcohol still intact), as I thought it couldn't be done with alpha, beta unsaturated ketones

I have manipulation of the enone before Beckmann rearrangement.
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Offline AlphaScent

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Re: Organic synthesis
« Reply #18 on: July 23, 2013, 10:25:48 AM »
Where does that methyl group come from.  I understand the first 4 steps.  Oxidize, aldol, beckman, hydrolyze.  I am missing something and I dont know where.  Dehydration? Then friedel-crafts? 
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Offline AlphaScent

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Re: Organic synthesis
« Reply #19 on: July 23, 2013, 11:28:42 AM »
No friedel Crafts, but this is what I have.  Understand most of it, but the middle with beckmann and the methyl group is confusing.

This is what I have for a scheme.  See attached.
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Offline orgopete

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Re: Organic synthesis
« Reply #20 on: July 23, 2013, 03:05:39 PM »
Me too, and cuprate for missing.
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Offline AlphaScent

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Re: Organic synthesis
« Reply #21 on: July 24, 2013, 10:27:13 AM »
Cuprate for missing methyl.  Got it.  What he has written in his sythesis is the Gilman reagent, lithium dimethylcuprate.  Which according to wikipedia, it uses primary alkyl halides to complete the carbon carbon bond formatiom.  Just as a learning experience, can you point in the direction where the methylation is selective for that type of reaction using a cuprate?
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Offline magician4

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Re: Organic synthesis
« Reply #22 on: July 24, 2013, 10:26:31 PM »
one question that still puzzles me...: with the Beckmann rearrangement, how do we steer which side the amine (amide) will be oriented to? any thermodynamic reason why it should be connected to the 5-membered ring by the end of the day?

hmmm...

still curious what your ideas might be insofar


regards

Ingo

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Offline Dan

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Re: Organic synthesis
« Reply #23 on: July 25, 2013, 03:11:38 AM »
Quote from: magician4 on July 24, 2013, 10:26:31 PM
one question that still puzzles me...: with the Beckmann rearrangement, how do we steer which side the amine (amide) will be oriented to? any thermodynamic reason why it should be connected to the 5-membered ring by the end of the day?

The group trans to the oxime OH will migrate - the bulkier group is usually in this position.
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Offline magician4

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Re: Organic synthesis
« Reply #24 on: July 25, 2013, 01:54:20 PM »
Quote
(...)the bulkier group is usually in this position.

this would open the question which ring would be of more sterical demand with respect to the nitrogen position (hence leading to a respective hydroxyl-group orientation): 5 or 7 membered ring?

I'd call this a close shave

anything I'm missing here?


regards


Ingo
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Offline Dan

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Re: Organic synthesis
« Reply #25 on: July 25, 2013, 05:30:40 PM »
Considering the oxime, you should get a strong preference for E configuration - methylene substituent vs cyclopentyl, the latter is significantly bulkier I would expect. This would lead to the desired cyclopentylamine.
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