[asa029]

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).

[g-bones]

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.

[superg]

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?

[OC pro]

just wondering: by adding a lithio acetylide on an aldehyde, won't you get the corresponding propargylic alcohol?

Of course.

[asa029]

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.

[asa029]

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!

[fledarmus]

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.