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Topic: ylid preparation  (Read 3917 times)

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Offline GSK

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ylid preparation
« on: October 01, 2006, 06:35:17 PM »
I wonder if anyone has any helpful suggestions. I am trying to prepare triphenylphosphoranylidene crotonaldehyde (a 4-carbon ylid with two conjugated double bonds, one from the alpha carbon to P, and terminating in an aldehyde) from the corresponding bromide Wittig salt (which was prepared from bromocrotonaldehyde, E-double bond). The only literature reference I can find is a Tet. Lett from the early 1980s and all it basically says is that the ylid was liberated from the salt in CH2Cl2 with cold 1M NaOH, then the crude extract was triturated with cold acetone. I have tried this and it will not work. The only solid I can triturate is a brown amorphous powder that has a m.p. 10C higher than the lit value; this isn't the desired product as it doesn't react as expected. I am confident that the starting bromide salt is the correct material (based on m.p.). Anyone have any tips?
 
 
 

Offline Borek

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Re: ylid preparation
« Reply #1 on: October 01, 2006, 06:56:19 PM »
Anyone have any tips?

Yes. Please don't cross post.
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Offline GSK

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Re: ylid preparation
« Reply #2 on: October 01, 2006, 07:01:24 PM »
I sent a PM to the moderator asking for my cross posts to be removed as I did it by accident.  ???

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Re: ylid preparation
« Reply #3 on: October 02, 2006, 11:34:46 AM »
You can deprotonate the salt with some other base like potassium t-butoxide, sodium hydride, or butyllithium.  Then don't do the trituration part, just add a solution of your ketone/aldehyde to the solution of your ylide.  You probably want to use an excess of your salt and slightly less than a full equiv of base relative to salt.  You'll have to run everything pretty dry if you use these conditions as well.

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