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Intramolecular 1,8‐Hydrogen‐Atom Transfer Reactions in (1→4)‐ O ‐Disaccharide Systems: Conformational and Stereochemical Requirements
Author(s) -
Francisco Cosme G.,
Herrera Antonio J.,
Kennedy Alan R.,
Martín Angeles,
Melián Daniel,
PérezMartín Inés,
Quintanal Luis M.,
Suárez Ernesto
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200801414
Subject(s) - intramolecular force , chemistry , pyranose , disaccharide , hydrogen atom , hydrogen atom abstraction , stereochemistry , ring (chemistry) , isomerization , hydrogen , organic chemistry , catalysis , alkyl
The stereochemical and conformational factors controlling the intramolecular hydrogen‐atom transfer (HAT) reaction between the two pyranose units in a (1→4)‐ O ‐disaccharide when promoted by a primary 6‐ O ‐yl radical are studied. Models with α‐ D ‐Glc p ‐(1→4)‐β‐ D ‐Glc p , α‐ L ‐Rham p ‐(1→4)‐α‐ D ‐Gal p or α‐ D ‐Man p ‐(1→4)‐β‐ L ‐Gul p skeletons led exclusively to the abstraction of the hydrogen from HC‐5′ and the formation, through a nine‐membered transition state, of a 1,3,5‐trioxocane ring system in a stable boat–chair conformation. Notwithstanding, derivatives of α‐ L ‐Rham p ‐(1→4)‐α‐ D ‐Glc p or α‐ D ‐Man p ‐(1→4)‐α‐ D ‐Gal p exclusively abstract the hydrogen from HC‐1′ through a seven‐membered transition state and, therefore, lead to an interglycosidic spiro ortho ester.