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Topic: Give me tips for this synthesis problem?  (Read 374 times)

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Offline sharbeldam

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Give me tips for this synthesis problem?
« on: May 02, 2020, 09:15:17 AM »
I tried, but I got stuck. I cant do a wolff kishner, And I think I also started wrong since the major product didnt really help me.
Any tips?
problem attached.
(the first step is lindlar)
« Last Edit: May 02, 2020, 09:30:04 AM by sharbeldam »
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Offline rolnor

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Re: Give me tips for this synthesis problem?
« Reply #1 on: May 02, 2020, 10:15:32 AM »
How about use Lindlar, then Pd(PPh4) to isomerize/move the double bond into the ring as a start?

Offline sharbeldam

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Re: Give me tips for this synthesis problem?
« Reply #2 on: May 02, 2020, 10:52:51 AM »
I appreciate that rolnor, but This reaction is not included in the syllabus and I am as a tutor still not familiar with it. Id be happy for a link that explains it.

Any other ways? in my idea, it does make the double bond to the left but the problem is that it wouldnt be the major product :/
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Offline rolnor

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Re: Give me tips for this synthesis problem?
« Reply #3 on: May 02, 2020, 01:41:18 PM »
Here is a link:

https://pubs.rsc.org/en/content/articlelanding/2019/cc/c9cc00223e#!divAbstract

The double bond in this case should migrate into the ring I think. Then the next step would be ozonolysis.

Offline sharbeldam

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Re: Give me tips for this synthesis problem?
« Reply #4 on: May 02, 2020, 05:42:10 PM »
Ok this is what I did, Id get aldehyde and ketone in the chain tho. I want to turn the aldehyde into halide without touching the ketone . ill keep thinking of it :D
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Offline rolnor

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Re: Give me tips for this synthesis problem?
« Reply #5 on: May 03, 2020, 03:15:50 AM »
OK, I see now that you have the ozone-step. To reduce aldehyde in presence of ketone should be possible, maybe NaBH3CN att the right pH?

Offline sharbeldam

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Re: Give me tips for this synthesis problem?
« Reply #6 on: May 03, 2020, 03:39:23 PM »
I thought it reduces imines but not ketones and aldehydes, so its more selective to aldehydes?
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Offline rolnor

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Re: Give me tips for this synthesis problem?
« Reply #7 on: May 03, 2020, 04:05:24 PM »
If you have a little more acidic conditions it will reduce aldehydes selective but I am not sure about the pH. Also diisobutylaluminiumhydride at -78 could work.

Offline rolnor

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Re: Give me tips for this synthesis problem?
« Reply #8 on: May 03, 2020, 04:08:17 PM »

Offline hollytara

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Re: Give me tips for this synthesis problem?
« Reply #9 on: May 03, 2020, 10:47:37 PM »
Will BH3-THF reduce the ketone?  It will reduce an acid - so if you cleave 1-ethylcyclopentene with permanaganate instead of ozone to get the ketone and acid, you can then reduce the acid with BH3-THF and make the alcohol.  The mechanism of reduction is complex, but it works for acids but not esters or ketones or aldehydes.  (While you can't reduce a ketone by itself with BH3, I am not certain that if you have both a ketone and an acid that reduction will be selective - the triacetoxyborane that rolnor suggests is a lot like the intermediate in the acid reduction.)

But I think they teach it at the sophomore level as being selective for acids. 



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