Carbohydrates U 0500Stereoselective Synthesis of 1,3-Disaccharides Through Diels-Alder Reactions. Part 2. Convenient Protecting Groups for Heterodienes and Conformational Evaluations. -Enantiopure β-keto-δ-lactones like (IV) are obtainable from glycals avoiding tedious and time-consuming protection-deprotection reactions. Silylidene as well as phenylsulfonylethylidene protecting groups are stable under the conditions employed. Silylidene-lactone (IV) is transformed into a thione intermediate and reacts as heterodiene in an inverse electron-demand cycloaddition yielding disaccharide (VI). The phenylsulfonylethylidene-protected disaccharide (IX) is prepared in a similar manner, albeit in lower yield. In addition, the first example of a β-oxy-imino-δ-lactone (XII), synthesized from β-keto-δ-lactone (X), is also reported. -(GABRIELLI, G.; MELANI, F.; BERNASCONI, S.; LUNGHI, C.; RICHICHI, B.; ROLLIN, P.; VENTURI, C.; NATIVI*, C.; J. Carbohydr. Chem. 28 (2009) 1-3, 124-141; Dip. Chim. Org., Univ. Stud. Firenze, I-50019 Sesto Fiorentino, Italy; Eng.) -H. Hoennerscheid 39-189
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