[Embark04]

Hi:

I am new to this site, but am finding it to be a great asset to have.

I am running a Birch reduction on an allylic benzyl ether (deprotection). As a test reaction, I condensed the ammonia in a flask and added my starting material. I then added very small pieces of Na until the blue color persisted. I noticed that it took ~10-15 minutes to dissolve the thin strips of metal before the solution became clear again. In all, it took about an hour to see a persistant blue color (I think this is too long for a substrate to be swimming along with free electrons).

As such, I ended up isolating byproduct. The reaction itself was very clean. My questions are:

a. I am guessing that I should have added my substrate in at the end (dissolved in THF), after the solution had a persistent blue color. I think that I formed my deprotected alcohol (by TLC), but it subsequently underwent some kind of rearrangement.
b. I dont understand why the blue color should persist. These reactions should be "relatively quick" such that the reaction occurs with every addition of sodium.
c. Does anyone know if allylic benzyl ethers are poor substrates for this reaction?

Thanks for any input!

[discodermolide]

Hi:

I am new to this site, but am finding it to be a great asset to have.

I am running a Birch reduction on an allylic benzyl ether (deprotection). As a test reaction, I condensed the ammonia in a flask and added my starting material. I then added very small pieces of Na until the blue color persisted. I noticed that it took ~10-15 minutes to dissolve the thin strips of metal before the solution became clear again. In all, it took about an hour to see a persistant blue color (I think this is too long for a substrate to be swimming along with free electrons).

As such, I ended up isolating byproduct. The reaction itself was very clean. My questions are:

a. I am guessing that I should have added my substrate in at the end (dissolved in THF), after the solution had a persistent blue color. I think that I formed my deprotected alcohol (by TLC), but it subsequently underwent some kind of rearrangement.
b. I dont understand why the blue color should persist. These reactions should be "relatively quick" such that the reaction occurs with every addition of sodium.
c. Does anyone know if allylic benzyl ethers are poor substrates for this reaction?

Thanks for any input!

You are going to reduce the benzene ring as well. Usually one adds the SM last.
I would recommend looking at Greene's book on functional group protection for a better method.

[OC pro]

The best method for deprotection of allyl ether uses Pd(0). Perfect for your simple substrate...

H. Tsukamoto, T. Suzuki, Y. Kondo, Synlett, 2007, 3131-3132.

http://www.organic-chemistry.org/protectivegroups/hydroxyl/allyl-ethers.htm