[g_orbital]

Hi,

The following rxn (taken from Tetrahedron 2007, 63, 8499-8513) utilizes potassium carbonate in methanol for selective removal of N-Boc protecting group from the oxindole nitrogen. My question is: How could this selectivity be achieved, that the other N-Boc (of the oxazoline ring) remains unreacted? I understand that some electronic factors play cruical role here, but I fail to figure out how. Also, What is the mechanism of this interesting Boc-cleavage?

I'll appreciate your kind assistance.
Thank you very much indeed!

[AWK]

http://www.arkat-usa.org/?VIEW=MANUSCRIPT&MSID=1387

[g_orbital]

First of all, thank you AWK for the article!
Although the authors made use of another mild base (cesium carbonate, with imidazole in acetonitrile), it seems that this method works in the same manner. I also found another article (JOC 2003, 68, 743-746) which deals with LiBr or Mg(ClO₄)2 in acetonitrile for that purpose.

However, the fundamental question remains unanswered: what are the electronic reasons responsible for this reactivity difference, i.e. why is only this N-acetylcarbamate (the oxyindole nitrogen) affected, while the oxazoline N-Boc is not cleaved?

Thanks again!

[AWK]

Did you note in my link BOC group close to carbonyl group is removed easily and this is explained in this link.