Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: asa029 on April 16, 2012, 02:09:28 AM
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Hi everyone!
I want to deprotonate a terminal alkyne and react it with an aldehyde to give the Favorskii adduct. I am therefore looking for suitable bases to do this reaction. Everyone always talks about sodium amide (NaNH2) or LDA. I have worked with LDA before and it's not my best friend, so I was wondering if anyone had any experience with sodium amide in this type of reaction (especially concerning handling).
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Unless you have other sensitive functionality on your alkyne, you can just butyl lithium directly, then quench with your aldehyde to get your 1,2-addition adduct.
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n-BuLi works well, at 0°C in THF. i'll on consider using LDA if there is possibility of addition on another part of your molecule.
just wondering: by adding a lithio acetylide on an aldehyde, won't you get the corresponding propargylic alcohol?
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just wondering: by adding a lithio acetylide on an aldehyde, won't you get the corresponding propargylic alcohol?
Of course.
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just wondering: by adding a lithio acetylide on an aldehyde, won't you get the corresponding propargylic alcohol?
Of course.
But it will likely enolize into the alfa, beta-unsaturated ketone after quenching with weak acid.
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Unless you have other sensitive functionality on your alkyne, you can just butyl lithium directly, then quench with your aldehyde to get your 1,2-addition adduct.
I have a tosylate which doesn't love base. One of the professors here said buli would be a "dead end", but he didn't explain why!
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Unfortunately, the n-butyl anion is also a good nucleophile. If there are available leaving groups, you will get substitution reactions.
Deprotonated amines are not particularly good nucleophiles and don't typically have this problem.
If you really need a base stronger than metal amides, you can use phenyllithium or in the worst case, t-butyllithium, but t-butyllithium is almost too reactive to handle.