Gaining access to stereodefined 2-deoxy-sugar containing oligosaccharides remains a formidable challenge.  This is largely due to the difficulties associated with controlling the selectivity of glycosylations using 2-deoxy-sugar donors.  As part of a program aimed at developing stereoselective routes to 2-deoxy-sugar containing linkages, we have developed an a-selective dehydrative glycosylation promoted by 3,3-dibromo-1,2,-diphenycyclopropene and tetrabutylammonium iodide (TBAI).  The method works with a range of glycosyl acceptors, and both D- and L- sugars show similar levels of selectivity (typically >10:1 a:�).  To showcase the method, we have used it to synthesize the tetrasaccharide fragment of the anthracycline antibiotic arugomycin.  We have also found that sulfur and carbon nucleophiles are competent acceptors in the reaction.  In the case of carbon nucleophiles, the reaction proceeds through an elimination/Ferrier rearrangement sequence to afford the 2,3-unsaturated C-glycosides.  The scope of this method and its application to oligosaccharide synthesis will be discussed.

Cyclopropenium cation mediated glycosylation with 2-deoxy-sugars for α-selective reactions

245th National Meeting (2013)

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