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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: xshadow on September 02, 2020, 07:23:57 AM

Title: LDA - kinetic or thermodynamic enolate (diketone)
Post by: xshadow on September 02, 2020, 07:23:57 AM
Hi

In my book I 've seen the first example of the following picture:
(https://i.imgur.com/l0BvkNr.jpg)

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!!!

Title: Re: LDA - kinetic or thermodynamic enolate (diketone)
Post by: spirochete 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.