ORGN 600 |
| Septanoses are unnatural seven membered ring carbohydrates that have the potential to adopt a number of low energy conformations. The greater flexibility of septanoses in comparison to their natural pyranose counterparts makes them attractive as models for studying carbohydrate-carbohydrate, carbohydrate-protein and carbohydrate-DNA interactions. Recent approaches towards the synthesis of septanose sugars have utilized carbohydrate based oxepines. While methods providing access to carbohydrate based oxepines often do so in good yield, they tend to suffer from several drawbacks including the use expensive catalysts, rigorous reaction conditions, and functional group specificity. As part of an ongoing effort to provide a more accessible approach to carbohydrate oxepines, and therefore septanoses carbohydrates, a transition metal catalyzed isomerization-ring closing metathesis route was explored. Four major sugars (2,3,4,6-tetra-O-benzyl-D-glucose, 2,3,4,6-tetra-O-benzyl-D-galactose, 2,3,4,6-tetra-O-benzyl-D-mannose, and 3,4,6-tri-O-benzyl-2-deoxy-D-glucose) were individually subjected to Wittig olefination, allylation, and bond migration using two different rhodium catalysts (Rh(I) and Rh(II)) and one ruthenium catalyst (Ru(II)) under various reaction conditions. Initial investigations revealed that sugar derivatives incorporating an unsubstituted allyl group migrated preferentially in the presence of a rhodium (I) and a strong base such as n-butyllithium. In contrast, sugar derivatives incorporating a substituted allyl group migrated preferentially in the presence of a rhodium (II) catalyst and a weaker base such as diisopropylethylamine. Although the ring closing metathesis of these molecules has yet to be attempted, it is speculated that the substituted allyl group may make it more favorable for Grubbs catalyzed ring closing metathesis to occur.
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Materials, Devices and Switches, Metal-Mediated Reactions, Asymmetric Reactions, Total Synthesis, Biologically-Related Molecules and Processes
7:00 PM-9:00 PM, Wednesday, April 9, 2008 Morial Convention Center -- La Louisiane, Blrm. C, Poster
Sci-Mix
Division of Organic Chemistry |
