[dopey1]

I want to reduce an aromatic carboxylic acid to an aldehyde and was thinking of the stevens reduction but casnt find a good prep for it. Anyone know of a reference or of another prep i could use. The reduction needs to be selective as there are other reducable groups in the molecule.
Cheers

[movies]

These are the references for the McFadyen-Stevens reduction (I assume it's the same one) in one book I have.  I haven't looked at these papers, but it's a start:

Tetrahedron Lett. 1966, 2927.
J. Heterocycl. Chem. 1975, 12, 1225.
J. Heterocycl. Chem. 1976, 13, 841.
J. Chem. Soc., Chem. Commun. 1978, 793.
Tetrahedron Lett. 1980, 21, 4645.
Synth. Commun. 1998, 28, 9.

[Doxorubicin]

Esterification followed by LAH reduction would yield a benzyl alcohol.   The aldehyde can be obtained in high yield and in less than an hour when the alcohol is oxidized with bleach in EtOac solvent with PTC.  Sorry I do not have the reference on hand for this.  

[movies]

I thought bleach did aldehyde to acid, not alcohol to aldehyde, at least that's what I have in my notes.

I think perhaps the reagent you are thinking of is Dess-Martin periodinane, which is often used in conjunction with bleach to go from alcohol to aldehyde and then to acid.

I'm guessing that LAH would be too powerful for the molecule in question in this thread.

[Donaldson Tan]

How about NaBH₄?

[movies]

NaBH4 isn't strong enough to reduce an acid to an aldehyde or alcohol on its own.  There is one curious reaction though were you add iodine to the mix and it can reduce an acid to an alcohol.  As far as I can tell no one knows why it works, but I can tell you that it does.  That might be a good alternative to the LAH in the suggestion above.

Here's a reference for the NaBH4 + iodine trick:

J. Org. Chem. 58, 3568 (1993).

http://pubs.acs.org/cgi-bin/archive.cgi/joceah/1993/58/i13/pdf/jo00065a020.pdf

[Doxorubicin]

Lithium borohydride can be generated in situ and is able to reduce esters to alcohols just as LAH.  I have never reduced an aromatic acid with this method so I cannot say much more than that.


As far as oxidation of the benzyl alcohol with bleach goes, only the aldehyde is obtained, not the acid.  This is in contrast to aliphatic alcohols which are oxidized further.

[java]

 
A simple Method for the reduction of Carboxylic Acids to Aldehydes or alcohols using H2 and Pd/C

J.Org. Chem. 64, 8962-8964, 1999    

[yufgyfyu]

 I think it might be possible to reduce carboxylic acids to aldehydes with Cah2. Like this,   


      2 RCOOH + CaH2  ---->  2 RCOH + Ca(OH)2

[discodermolide]

I want to reduce an aromatic carboxylic acid to an aldehyde and was thinking of the stevens reduction but casnt find a good prep for it. Anyone know of a reference or of another prep i could use. The reduction needs to be selective as there are other reducable groups in the molecule.
Cheers

Look for the Rosenmund reduction of acid chlorides, selective, mild and high yielding.

[BobfromNC]

It is very difficult to stop at the aldehyde, especially from the acid, even more so with the aromatic acid.   It would be better to either make the t-butyl thiol ester and reduce with DiBAL at low temp to make the aldehyde (warning, this will smell like a natural gas leak), or better, just reduce down to the alcohol and oxidize via Swern or Dess-Martin.   I am doing similar work right now, and it is nearly impossible to geta good yield of an aldehyde in one step.   You can get better yields in two steps of reduce and reoxidize to ald. than any prep that I have found.

Bob

[discodermolide]

It is very difficult to stop at the aldehyde, especially from the acid, even more so with the aromatic acid.   It would be better to either make the t-butyl thiol ester and reduce with DiBAL at low temp to make the aldehyde (warning, this will smell like a natural gas leak), or better, just reduce down to the alcohol and oxidize via Swern or Dess-Martin.   I am doing similar work right now, and it is nearly impossible to geta good yield of an aldehyde in one step.   You can get better yields in two steps of reduce and reoxidize to ald. than any prep that I have found.

Bob

Reduction of the acid chloride with a Pd/BaSO4 cat and H2 stops at the aldehyde and does NOT reduce further. I've done this on very large scale >100kg many times with a large variety of acids

[Åke]

I want to reduce an aromatic carboxylic acid to an aldehyde and was thinking of the stevens reduction but casnt find a good prep for it. Anyone know of a reference or of another prep i could use. The reduction needs to be selective as there are other reducable groups in the molecule.
Cheers

Look for the Rosenmund reduction of acid chlorides, selective, mild and high yielding.

A lesser known alternative to Rosenmund reduction is a very mild method known as Fukuyama reduction. It proceeds via thioester which has to be prepared first. Triethylsilane acts as a hydride source but nucleophiles other than hydride can be used e.g. organozinc derivatives. For literature on Fukuyama reduction check http://www.organic-chemistry.org/namedreactions/fukuyama-reduction.shtm