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Offline mintyrogue

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Synthesis question
« on: April 13, 2015, 10:21:41 PM »


For this question, so far I think that I should remove the ketone group using the Wolff Kishner reaction.

However, I'm unsure of how to add the alkyl group.  Should I use FC Alkylation?  If this is correct, how would I make the position on the cyclohexane ring nucleophilic?
I was also wondering if I could remove Bromine and form a double bond, then using FC alkylation?

Thank you in advance!

Offline Dan

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Re: Synthesis question
« Reply #1 on: April 14, 2015, 03:34:02 AM »
However, I'm unsure of how to add the alkyl group.  Should I use FC Alkylation?  If this is correct, how would I make the position on the cyclohexane ring nucleophilic?

Well, there is a general problem with using F-C alkylation to introduce an isobutyl group - look up the behavior of isobutyl chloride in F-C alkylation. In any case, as far as I am aware F-C type alkylation does not work with unactivated alkenes.

Quote
For this question, so far I think that I should remove the ketone group using the Wolff Kishner reaction.

You are right that the ketone must be reduced at some stage, but removing this functionality at the start of the synthesis is a bad idea - it is a source of useful electrophilic reactivity.

Quote
I was also wondering if I could remove Bromine and form a double bond

Elimination of HBr to form an alkene is a good idea...
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Offline mintyrogue

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Re: Synthesis question
« Reply #2 on: April 17, 2015, 12:33:45 PM »
However, I'm unsure of how to add the alkyl group.  Should I use FC Alkylation?  If this is correct, how would I make the position on the cyclohexane ring nucleophilic?

Well, there is a general problem with using F-C alkylation to introduce an isobutyl group - look up the behavior of isobutyl chloride in F-C alkylation. In any case, as far as I am aware F-C type alkylation does not work with unactivated alkenes.

Quote
For this question, so far I think that I should remove the ketone group using the Wolff Kishner reaction.

You are right that the ketone must be reduced at some stage, but removing this functionality at the start of the synthesis is a bad idea - it is a source of useful electrophilic reactivity.

Quote
I was also wondering if I could remove Bromine and form a double bond

Elimination of HBr to form an alkene is a good idea...

Thank you for the response!  I'm still stuck on the isobutyl addition.  I know that if I use FC alkylation there would be a hydride shift when the carbocation intermediate is formed, so I'm not sure how to add this group onto the ring.

Offline pgk

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Re: Synthesis question
« Reply #3 on: April 17, 2015, 12:56:40 PM »
Usually, FC alkylation works badly with cycloalkenes. The reason is that Lewis acid catalysis leads to anionic polymerization byproducts. Think about a nucleophilic attack to double bond. 

Offline Dan

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Re: Synthesis question
« Reply #4 on: April 18, 2015, 05:07:54 AM »
Try elimination of HBr as the first step.
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Offline orgopete

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Re: Synthesis question
« Reply #5 on: April 18, 2015, 09:00:14 AM »
Do you know 1,4-conjugate addition reactions?
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Offline mintyrogue

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Re: Synthesis question
« Reply #6 on: April 19, 2015, 12:07:45 PM »
Do you know 1,4-conjugate addition reactions?

I didn't think of that!  So, I would eliminate HBr to form the alkene and use Gilman's reagent?

Thank you!

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