[endophytic]

Hi all !

I'm new on the forum :p

Which alternative reduction condition would you suggest me to pass from a carboxylic acid to alcohol, and not reducing neither a double bond nor a ketone present on my compound ?

(I've esterified the acid, and tried to reduce it with NaBH4 in THF at 70 C)


Thank you !

[Doc Oc]

1) Anything that will reduce an ester will reduce a ketone, you will need to protect that as a ketal.

2) If the alkene is in conjugation with either carbonyl you will have troubles.

3) NaBH₄ is not strong enough to reduce esters, you need to use something stronger like LiAlH₄ or DIBAL.

[endophytic]

Hello Doc Oc !

Thx for the quick reply.
The double bond isn't cojungated so it shouldn't be a problem.
In fact Ihve tried NaBH4 thinking it was softer than LiAlH4, I saw here http://gaussling.wordpress.com/2007/04/07/nabh4-reduction-of-esters/ (see article by de Souza) that it was possible so tried this.. but did not think about the ketone :/

Haven't determined the products yet but effectively it's very probable that the ketone will be reduced.
So protection of this function is necessary ? (Another strange/stupid question maybe ..; is the fact that a ketone is engaged in a H bond with, lets say and adjacent OH modify the initial reactivity of the ketone ?)

Again thank for the quick replie  

[discodermolide]

1) Anything that will reduce an ester will reduce a ketone, you will need to protect that as a ketal.

2) If the alkene is in conjugation with either carbonyl you will have troubles.

3) NaBH₄ is not strong enough to reduce esters, you need to use something stronger like LiAlH₄ or DIBAL.

NaBH4 will reduce esters. I've done it many times on >500kg scales

[Doc Oc]

Yes, you absolutely need to protect the ketone, the hydrogen bonding will not save it.

It sounds like you can use NaBH₄ for the reduction, but the ketone will still be reduced.  In fact, it will be reduced before the ester, so take the proper precautions.