摘要 : The stereochemical and conformational factors controlling the intramolecular hydrogen-atom transfer (FIAT) reaction between the two pyranose units in a (1 -> 4)-O-disaccharide when promoted by a primary 6-O-yl radical are studied.... 展开 The stereochemical and conformational factors controlling the intramolecular hydrogen-atom transfer (FIAT) 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. Notwith-standing, derivatives of alpha-L-Rhamp-(1 -> 4)-alpha-D-Glcp 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. 收起