β-Selective C-Glycosylation and its Application in the Synthesis of Scleropentaside A.

C-Glycosides are carbohydrates that bear a C-C bond to an aglycon at the anomeric center. Due to their high stability towards chemical and enzymatic hydrolysis, these compounds are widely used as carbohydrate mimics in drug development. Herein, we report a general and exclusively beta-selective method for the synthesis of a naturally abundant acyl-C-glycosidic structural motif first found in the scleropentaside natural product family. A Corey-Seebach umpolung reaction as the key step in the synthesis of scleropentaside A and analogues enables the beta-selective construction of the anomeric C-C bond starting from unprotected carbohydrates in only four steps. The one-pot approach is highly atom-efficient and avoids the use of toxic heavy metals.