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The stereochemical and conformational factors controlling the intramolecular hydrogen atom transfer (HAT) reaction between the two pyranoseunits in a (1
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4)-disaccharide when promoted by a primary 6-
O-yl radical are studied. Models with
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-
D-Glc
p-(1
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4)-
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-
D-Glc
p or
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-
L-Rham
p-(1
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4)-
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-
D-Gal
p skeletons lead exclusively to the abstraction of H-C-5' and the formation, through a nine-membered transition state, of a1,3,5-trioxocane ring system in a stable boat-chair conformation. Notwithstanding, derivatives of
![](/images/gifchars/alpha.gif)
-
L-Rham
p-(1
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4)-
![](/images/gifchars/alpha.gif)
-
D-Glc
p abstract exclusivelyH-C-1' through a seven-membered transition state and therefore lead to an interglycosidic spiro ortho ester.