[taurean]

Any suggestions about this particular transformation are highly appreciated.  Image of the reaction attached as gif file.

[movies]

You can probably do that with the Noyori Ru/BINAP system, although it actually reduces the keto form, not the enol form.

Check out JACS 1989, 111, 9134.

[Custos]

That wouldn't give any stereocontrol over the carboxylate though right? If you really need this you could try locking the double bond as a silyl enol ether then use catalytic hydrogenation (e.g. palladium). The fused ring system should protect the bottom face to give hydrogen addition from the other side. That gets the carboxylate right but the alcohol stereochemistry will need to be inverted, say with a Mitsunobu.

[taurean]

You can probably do that with the Noyori Ru/BINAP system, although it actually reduces the keto form, not the enol form.

Check out JACS 1989, 111, 9134.

Thanks movies.  Noyori Ru/BINAP is a chiral catalyst.  Can we use this catalyst for the diastereoselective reduction of the racemic starting material?

[taurean]

That wouldn't give any stereocontrol over the carboxylate though right? If you really need this you could try locking the double bond as a silyl enol ether then use catalytic hydrogenation (e.g. palladium). The fused ring system should protect the bottom face to give hydrogen addition from the other side. That gets the carboxylate right but the alcohol stereochemistry will need to be inverted, say with a Mitsunobu.

Thanks for the suggestion Custos.  I was also thinking on the same lines using Mitsunobu to invert the stereocenter.  However, I am not sure if it effects the carboxylate stereocenter during the inversion.  I used Pd in one of the reactions to reduce the double bond, it did not effect the enol.  I have to try someother transition metal.

[movies]

That wouldn't give any stereocontrol over the carboxylate though right?

Yes it does!  Noyori observed almost perfect diastereoselectivity.  You should check out the paper, they have an interesting transition state proposal for why the d.r. is so high despite the fact that the reduction occurs on a chiral molecule.

Thanks movies.  Noyori Ru/BINAP is a chiral catalyst.  Can we use this catalyst for the diastereoselective reduction of the racemic starting material?

The only thing you would have to worry about is kinetic resolution.  One of the enantiomers of your product may react a lot more slowly than the other.  The Noyori reduction usually overrides the stereochem of the starting material, so it might also be that both enantiomers would be reduced enantioselectively and give products which are diastereomers.

Another option may be to use racemic BINAP as ligand.  I don't know exactly what would happen, but you might get exactly what you want: diastereoselective reduction without resolution.

[kiwi]

don't forget Myers handout for a gentle introduction to the Noyori conditions (including dynamic kinetic resolution, which ideally is want you want here):

http://www-chem.harvard.edu/groups/myers/handouts/Noyori.pdf

[taurean]

don't forget Myers handout for a gentle introduction to the Noyori conditions (including dynamic kinetic resolution, which ideally is want you want here):

http://www-chem.harvard.edu/groups/myers/handouts/Noyori.pdf

Thanks kiwi for the nice handout of Myers.

[taurean]

[/quote]
The only thing you would have to worry about is kinetic resolution.  One of the enantiomers of your product may react a lot more slowly than the other.  The Noyori reduction usually overrides the stereochem of the starting material, so it might also be that both enantiomers would be reduced enantioselectively and give products which are diastereomers.
[/quote]

So, you mean to say that even if I use R or S BINAP, since Noyori reduction overrides stereochem of the starting material, I might get the racemic product???

The other thing I am concerned is, if I would be able to reduce the enol with Noyori's catalyst because of the inherent stability of that C=C.

[movies]

So, you mean to say that even if I use R or S BINAP, since Noyori reduction overrides stereochem of the starting material, I might get the racemic product???

The other thing I am concerned is, if I would be able to reduce the enol with Noyori's catalyst because of the inherent stability of that C=C.

No, if the catalyst overrides the stereochem then you would get two diastereomeric products, each of which would have high enantiomeric excess.

Like a said above, Noyori's catalyst reduces the keto tautomer, not the enol tautomer.  The interconversion of these two is rapid under most conditions, so it shouldn't be a problem.