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Topic: Retrosynthesis Question  (Read 2616 times)

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Offline escalona

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Retrosynthesis Question
« on: April 03, 2014, 06:41:19 PM »



Hi guys, I was wondering if you could help me figure this out.  The first image is a retrosynthesis question that indicates the number of steps (and intermediates) that should be taken in order to reach the desired product.  Unfortunately, after placing the -COOH group ortho to the -OH, step 4 indicates only one step is needed in order to make the ester or ether.
Is there anyway to create the ester or ether within one step?  Williamson Ether Synthesis requires deprotonation and then substitution and one would have to make the acyl chloride before reaction with the allylic bromide. 

Offline escalona

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Re: Retrosynthesis Question
« Reply #1 on: April 03, 2014, 06:53:37 PM »
I apologize, the acyl chloride shouldn't react with the allylic bromide in order to form the ester.
If anything is it possible for it to react with allyl alcohol, CH2=CHCH2OH?


Offline Dan

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Re: Retrosynthesis Question
« Reply #2 on: April 03, 2014, 07:09:58 PM »
Unfortunately, your synthesis falls apart at step 1.

1. Is NaOH a strong enough base to deprotonate a cyclohexanol on carbon?
2. What is the most acidic proton in cyclohexanol?

Hint: Why does enolate chemistry work?
My research: Google Scholar and Researchgate

Offline escalona

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Re: Retrosynthesis Question
« Reply #3 on: April 03, 2014, 07:19:34 PM »
I apologize.  I didn't realize the weak acidity of the -OH proton on cyclohexanol.  This question was given to us on a quiz, and we were taught the Kolbe-Schmitt reaction with phenols.  The -OH proton is much more acidic on a phenol.  I assume that it was a mistake to give us a non-aromatic ring, but assuming it was a phenol would the first 3 steps then be correct?

Offline Dan

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Re: Retrosynthesis Question
« Reply #4 on: April 04, 2014, 06:42:05 AM »
I assume that it was a mistake to give us a non-aromatic ring, but assuming it was a phenol would the first 3 steps then be correct?

That might be a risky assumption, but if the 6-membered ring is supposed to be aromatic throughout then your answer looks good to me.
My research: Google Scholar and Researchgate

Offline escalona

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Re: Retrosynthesis Question
« Reply #5 on: April 04, 2014, 07:32:04 AM »
Hi Dan,
Thanks for replying.  These quizzes are typically based on what we had been taught the previous week, which was Kolbe-Schmitt, but thank you for pointing for out that this would not occur with cyclohexanol.  I'll make sure to be aware of that with any mechanisms involving phenols and deprotonation.  Is it possible to create the ether or ester in one step?  If not, then if I had first created the ether, would KH react with the H+ on the carboxylic acid instead of on the ring?
Edit: It would, it's more acidic. Thanks for the help.
« Last Edit: April 04, 2014, 08:48:07 AM by escalona »

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