From: Jonas Nilsson (jonni$##$ifm.liu.se)
Date: Thu Aug 30 2001 - 09:59:13 EDT
I'm having some problems with catalytic hydrogenation of Z-protected
In a series of compounds I'm currently working on, my final step is
deprotection of the amidine.
The procedure involves treating my compounds with hydrogen gas in the
presence of Palladium 10% on activated carbon. I use ethanol with water
(5-10%) as solvent. Most of the compounds in the series goes without prob=
giving the desired amidine in good yield. However the last one seems almo=
impossible to deprotect in good yield.
This is to me quite confusing since there is very little difference in th=
structures, and no difference at all in the CBZ-part.
The general reaction look like this:
For the X part I've used:
They all worked fine. My latest addition was X=Ph-CH2-SO2- and this has
given me some problems.
From a 1/2-1 hour reduction I was now forced to reduce for 2 days with 3
additions of Pd/C to achieve approx. 50% of product among with 20%
startingmaterial and 10% of product missing the X part completly.
So, we all know that sulfur poisons palladium, but I've never heard of an
oxidized sulfur working as a poison.
I now turn to you and hope that you may shed some light on this problem
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