ORGLIST:sterically demanding N-alkylation

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From: Christoph D. Hahn (c.hahn$##$
Date: Wed Mar 03 2004 - 04:43:01 EST

Hi everybody!

I tried to bis-alkylate the free NH2-group of the tert.butyl ester of an
alpha-amino acid with bromoacetic acid tert.butyl ester, as in the
following scheme:

R-CH(NH2)-COO-t.Bu + 2 Br-CH2-COO-t.Bu -> R-CH[N(CH2-COO-t.Bu)2]-COO-t.Bu
solvent: DMF, catalyst: triethylamine

Bromoacetic acid tert.butyl ester was present in more than 10-fold excess
and triethylamine in about 7-fold excess. Still, whereas the monoalkylation
proceeded quickly, only 65 % of the substance were bisalkylated after 4
days' reaction at 50 C under an Ar atmosphere, although according to
literature the reaction should have been completed by that time.

Does anybody have experiences with that or a similar reaction?


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