1,3-Dipolar cycloaddition of exo-methylenesugars with nitrone:: approach to new amino-C-ketosyl disaccharides

Stereoselective 1,3-dipolar cycloadditions of exo-methylenesugars 1a-c to a sugar nitrone 2 were carried out with refluxing a toluene solution and afforded the corresponding cycloadducts, ketosyl spiro-isoxazolidine disaccharides 3a and 4a-c. Followed by reductive cleavage of the N-O bond of the isoxazolidine ring with the treatment of Zn-AcOH-Ac2O or with catalytic hydrogenation (Pd(OH)(2)/C), the cycloadduct 3a could be readily converted into a novel amino-C-disaccharide possessing a ketose form, providing an access to novel amino-C-ketosyl disaccharides. (C) 2004 Elsevier Ltd. All rights reserved.