chapter  5
6 Pages

Metal-Free Oxidative Lactonization of Carbohydrates Using Molecular Iodine

Diversely protected carbohydrate lactones are useful intermediates for synthesis of natural products, in particular for an easy access to C-glycosyl compounds.1-5 Concerning the oxidation of a hemiacetal function to produce lactones, only few high-yielding methods are known. Oxidative lactonization of free carbohydrates can be effected using bromine water and a BaCO3 buffer to form in situ the hypobromite/ bromate oxidative agents.6,7 Under these conditions, oxidation is selective at the anomeric position but suitable mainly to water-soluble compounds. Moreover, this methodology, when applied to unprotected sugars, generally provides a mixture of δ-and γ-lactones and glyconic acids. A similar procedure with molecular iodine has been developed and has the same disadvantages.8 The procedure used by Cordova and

Experimental Methods .............................................................................................34 General Method ...................................................................................................34 2,3,4-Tri-O-benzyl-d-xylono-1,5-lactone 2a ......................................................34 2,3,4,6-Tetra-O-benzyl-d-glucono-1,5-lactone 2b .............................................. 35

Acknowledgments ....................................................................................................36 References ................................................................................................................ 38

hemiacetal was selectively oxidized in presence of secondary hydroxyl groups.