December 05, 2021, 09:12:06 AM
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Topic: LDA - kinetic or thermodynamic enolate (diketone)  (Read 387 times)

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Offline xshadow

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LDA - kinetic or thermodynamic enolate (diketone)
« on: September 02, 2020, 07:23:57 AM »
Hi

In my book I 've seen the first example of the following picture:


Here LDA acts as a kinetic controller (deprotonation of the position with less steric hindrance)...as usually does


My doubts is for a diketone....here  I have a -CH2 between 2 C=O group

The deprotonation in that position gives the thermodynamic enolate ( large π-system)
Those two hydrogens are also far more acidic
But there is more steric hindrance


But there are also 2 groups of  terminal CH3 groups.
The corrispondent enolates are MUCH less stable and those hydrogens much less acid

But there is less steric hindrance

My question is:
Which enolate does   LDA form with  a diketone? the thermodynamic or the kinetic enolate?




Thanks!!!


Offline spirochete

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Re: LDA - kinetic or thermodynamic enolate (diketone)
« Reply #1 on: September 02, 2020, 11:00:53 AM »
I think LDA is an odd choice to deprotonate the 1,3-diketone. You don't need such a strong base. NaOH or NaOR would suffice for 99.999%  deprotonation. If LDA is used, I strongly suspect it will favor the thermodynamic enolate. Probably in the case of the 1,3-diketone, the thermodynamic and kinetic enolate are the same.

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