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Topic: **(HW) Help me synthesis 5-bromo-pentanal**  (Read 4423 times)

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Offline AO8onBLK

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**(HW) Help me synthesis 5-bromo-pentanal**
« on: April 26, 2010, 06:30:54 PM »

I am currently taking Organic II and need *delete me*

How can I turn Pentanal ... CH3CH2CH2CH2CH2(C=O)H into 5-bromo-pentanal

BrCH2CH2CH2CH2CH2(C=O)H.

I have tried NBS/Peroxide plus heat and just plain HBr, but my professor says this will not work!

What else will work!

Thanks in advance for your help.

Offline AO8onBLK

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Re: **(HW) Help me synthesis 5-bromo-pentanal**
« Reply #1 on: April 26, 2010, 10:12:46 PM »
Anyone?
 ???

Offline MissPhosgene

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Re: **(HW) Help me synthesis 5-bromo-pentanal**
« Reply #2 on: April 26, 2010, 10:15:10 PM »
Have you thought about radical reactions?
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Offline Smrt guy

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Re: **(HW) Help me synthesis 5-bromo-pentanal**
« Reply #3 on: April 26, 2010, 11:07:39 PM »
Are you sure you have the right starting material?  Activating an unactivated C-H bond is not easy in general, and radical reactions favor more substituted carbons.  Nothing comes immediately to mind to do this; the 2-position would be far more active in general.

Offline MissPhosgene

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Re: **(HW) Help me synthesis 5-bromo-pentanal**
« Reply #4 on: April 26, 2010, 11:24:03 PM »
Are you sure you have the right starting material? 

That is a good point.
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Offline orgopete

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Re: **(HW) Help me synthesis 5-bromo-pentanal**
« Reply #5 on: April 27, 2010, 01:02:29 AM »
This question asks us to guess what is being discussed in class. Okay, I am guessing enol chemistry. In order for that to work, you must convert the aldehyde into the unsaturated aldehyde by a bromination-dehydrobromination sequence. Then you can make a silyl enol ether, radical halogenation should give the more stable alkene, which I am guessing will place the bromine at the terminal position. Hydrolysis of the enol ether and catalytic reduction would give the product.

So, is the current topic enol chemistry?
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Offline MissPhosgene

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Re: **(HW) Help me synthesis 5-bromo-pentanal**
« Reply #6 on: May 03, 2010, 12:55:08 AM »
Did you learn about radical reactions like the Barton reaction?
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