Communication: The Reductive Coupling of Carbohydrate Radicals with Diazonium Ions: a New Access to 2-Amino-2-Deoxy Glycosides
Titel:
Communication: The Reductive Coupling of Carbohydrate Radicals with Diazonium Ions: a New Access to 2-Amino-2-Deoxy Glycosides
Auteur:
Bouhalbane, Elmahdi Veyrieres, Alain
Verschenen in:
Journal of carbohydrate chemistry
Paginering:
Jaargang 10 (1991) nr. 3 pagina's 487-492
Jaar:
1991
Inhoud:
The oxidative coupling of glycals with alcohols is an efficient procedure for creating an α-glycosidic bond. It can be triggered by an “I+”-reagent (iodonium di-sym-collidine perchlorate1 or N-iodosuccinimide2) and occurs in a 1,2-diaxial fashion through a presumed 1,2-iodonium ion intermediate leading to 2-deoxy-2-iodo-α-glycosides. This iodoglycosylation allows the preparation of 2-deoxy-α-glycosides by reductive deiodination with tributylstannane3 or nickel boride.4 Considering the behavior of good leaving groups at C-2 of α-D-mannopyranosides,5 the displacement of iodine by oxygen or nitrogen functions through SN2-type reactions would be difficult or impossible, unless performed with internal nucleophiles.6 In contrast, a C-2 radical can be easily trapped by electron-deficient olefins7 or nitrogen monoxide8 giving access to C-2 branched carbohydrates and oximes, respectively. Nucleophilic radicals have also been trapped by aryldiazonium ions in a reversible manner to give azo radical cations.9 In the presence of a reducing agent (Ti3+, Fe2+, Cr2+, V2+), the equilibrium is shifted towards the azo compound:
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