[Babcock_Hall]

A student I sometimes advise asked me "I have been trying the deprotection of 4 benzyl ethers on glucosamine with little progress. I have tried Pd/C in THF at atmospheric pressure using a Hydrogen balloon, and also at 70 psi in a hydrogenation parr jar.  I have seen some deprotection with the addition of MeOH and water.  Am I missing any key step that would hinder this reaction?"  I don't have much experience with this sort of chemistry, so I thought I should post something here.

[Dan]

Aliphatic amines can poison Pd catalysts - I encountered this problem many times in my years making iminosugars.

Solution: Run the reduction in dilute HCl. I used to use HCl in aqueous ethanol or dioxane with a HCl concentration of about 0.3 M as the reaction medium. It protonates the amines and stops them coordinating to Pd.

There should be examples of the procedure in this paper. Hope it works.

[Doc Oc]

Most of these palladium catalyzed reactions are pretty smooth, but they are subject to idiosyncrasies.

How old is the Pd/C?  It does go bad after long periods of time, so you could try just adding more.  In some cases, Pd/C isn't a strong enough catalyst.  I've found Pearlman's catalyst [Pd(OH)2] to be significantly more effective than Pd/C, that's also an option.  I've been able to use a hydrogen balloon at ambient pressure and temp with Pearlman's catalyst whereas the Pd/C reaction would have to be under high pressure.

MeOH is the most common solvent for these types of reactions, although I have used MeOH/THF blends.  Can't say I've ever just used THF.