Intramolecular 1,8-hydrogen-atom transfer reactions in (1-->4)-O-disaccharide systems: conformational and stereochemical requirements.
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 alpha-D-Glcp-(1-->4)-beta-D-Glcp, alpha-L-Rhamp-(1-->4)-alpha-D-Galp or alpha-D-Manp-(1-->4)-beta-L-Gulp skeletons led exclusively to the abstraction of the hydrogen from H--C-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 alpha-L-Rhamp-(1-->4)-alpha-D-Glcp or alpha-D-Manp-(1-->4)-alpha-D-Galp exclusively abstract the hydrogen from H--C-1' through a seven-membered transition state and, therefore, lead to an interglycosidic spiro ortho ester.
Francisco
Cosme G
CG
Instituto de Productos Naturales y Agrobiología del C.S.I.C. Carretera de la Esperanza 3, 38206 La Laguna, Tenerife, Spain.
Herrera
Antonio J
AJ
Kennedy
Alan R
AR
Martín
Angeles
A
Melián
Daniel
D
Pérez-Martín
Inés
I
Quintanal
Luis M
LM
Suárez
Ernesto
E
D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry; D004187:Disaccharides / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D015394:Molecular Structure; D013237:Stereoisomerism
D019086:Bridged Bicyclo Compounds, Heterocyclic; D004187:Disaccharides; D006859:Hydrogen