[CHEKAL]

how would i synthesise the resultant predominant generation of the relative stereochemistry of methyl butanoate-2-methyl,3-ol (image below). relative stereochemistry being OH and 2 methyl as dashed lines indicating different orientation to the other groups? The resultant product is to be racemic.

not sure if an aldol reaction would work in this case, as its an ester?

[discodermolide]

Why should the aldol reaction not work here?

[AlphaScent]

Why wouldnt it work?

What about LDA, -78 , THF?

What if it is done at a higher temperature? Say NaOH, reflux?

[CHEKAL]

i had doubt as its not an aldehyde but does have the carbonyl so it should work. Im just having difficulty in explaining/understanding the generation of the relative stereochemistry as i mentioned before. how would this reaction give that outcome and why would it be racemic?

[discodermolide]

The bonds having dashed lines are on the same side of the molecule. This presumable indicates a conformation where the steric interference between the two groups is minimised.
The molecule is racemic because you did not use anything chiral in your reaction. Racemic starting materials give racemic products.

[Dan]

how would i synthesise the resultant predominant generation of the relative stereochemistry of methyl butanoate-2-methyl,3-ol (image below). relative stereochemistry being OH and 2 methyl as dashed lines indicating different orientation to the other groups? The resultant product is to be racemic.

So, you want the syn-product?

I see problems with the aldol route.

1. You have an ester and an aldehyde, and you want to deprotonate the ester, and add it to the aldehyde. Problem here is that the aldehyde is much more acidic than the ester, so I would expect mainly self-condensation products of acetaldehyde if you added base to the mixture. 

2. You could attempt to deprotonate the ester with a strong base (e.g. LDA as suggested), and quench with acetaldehyde. First issue with this is suppression of Claisen condensation during the initial deprotonation step. Second problem is that LDA will give the E-enolate and consequently the anti-product according to the Zimmerman-Traxler model. The question asks for the syn-product. There are ways to make the Z-enolate, which should give the syn-product, but I would be concerned that in making this enolate you would see significant Claisen condensation.

Personally, I would make this from an acetoacetate derivative and not with aldol chemistry.

[CHEKAL]

Could I use a clauses condensation reaction to synthesise a b-keto ester then use a reducing agent, one equivalent, to reduce the keto group to a hydroxy group which would give me the b-hydroxy ester I require?

[orgopete]

Because stereochemistry is mentioned (but not drawn in the structure), this suggests several possible routes. We missed that class. Perhaps you could tell us what chemistry was being discussed in class, for example, Evans aldol reactions, asymmetric reductions, etc.

[CHEKAL]

we have been studying control of relative stereochemistry such as stereoselective aldol reactions in the cyclic intermediate with axial and equatorial interactions and Zimmerman-Traxler transitions states. I am investigation pathways that give a racemic compound and alternative pathways where enantiomeric excess occurs. In this thread I am trying to explain the generation of the racemic compound.

[Dan]

In this thread I am trying to explain the generation of the racemic compound.

So am I. To clarify, racemic ≠ a syn/anti mixture.

The syn and anti products are diastereomers, and both exist as a pair of enantiomers (so 4 stereoisomers are possible).

If the question asks for racemic syn, it is asking for conditions that will give selectively a 1:1 mixture of the two syn products and less of the two anti products. It is asking for diastereoselectivity, but not enantioselectivity - relative stereocontrol, but not absolute stereocontrol.

[CHEKAL]

it asks for the generation of the relative stereochemistry of the racemic product. Both OH and Methyl substituents are displayed as dashes that dont go to a point, indicating relative, so im guessing its going to be syn/syn : anti/anti products 50:50

[Dan]

it asks for the generation of the relative stereochemistry of the racemic product

If you generate both syn and anti, you have not controlled the relative stereochemistry.

It sounds to me like you have to make the racemic syn compound, but you will have to show us the picture to be sure.

[CHEKAL]

the picture you have just uploaded on the left is what i have, so it must be the syn compound as racemic