Efficient Generation of β‐ L ‐Rhamnosidic Linkages by the 2‐Ulosyl Donor Approach: Synthesis of a Trisaccharide with a Central β‐ L ‐Rhamnose Unit

Practical procedures for the production of variously blocked 6‐deoxy‐α‐ L ‐ arabino ‐2‐ketohexosyl bromides from L ‐rhamnose have been developed. These compounds are highly useful as indirect β‐ L ‐rhamnosyl donors: they undergo β‐specific glycosidations under Koenigs‐Knorr conditions, and the 2‐keto group of the resulting 6‐deoxy‐β‐ L ‐hexosiduloses is reduced with high β‐ L ‐ rhamno selectivity. The straightforward application of this 2‐ulosyl donor approach for the synthesis of β‐ L ‐rhamnose‐containing di‐ and trisaccharides is demonstrated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)