Intramolecular 1,8-hydrogen-atom transfer reactions in (1 -> 4)-o-disaccharide systems: conformational and stereochemical requirements

Francisco, C.G. and Herrera, A.J. and Kennedy, A.R. and Martin, A. and Melian, D. and Perez-Martin, I. and Quintanal, L.M. and Suarez, E. (2008) Intramolecular 1,8-hydrogen-atom transfer reactions in (1 -> 4)-o-disaccharide systems: conformational and stereochemical requirements. Chemistry - A European Journal, 14 (33). pp. 10369-10381. ISSN 0947-6539 (http://dx.doi.org/10.1002/chem.200801414)

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Abstract

The stereochemical and conformational factors controlling the intramolecular hydrogen-atom transfer (HAT) reaction between the two pyranose units in a (14)-O-disaccharide when promoted by a primary 6-O-yl radical are studied. Models with -D-Glcp-(14)--D-Glcp, -L-Rhamp-(14)--D-Galp or -D-Manp-(14)--L-Gulp 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 -L-Rhamp-(14)--D-Glcp or -D-Manp-(14)--D-Galp exclusively abstract the hydrogen from HC-1 through a seven-membered transition state and, therefore, lead to an interglycosidic spiro ortho ester.

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