Stereoselective approach to C-glycosylasparagines

In this paper we describe a simple and efficient approach to N-glycopeptide analogues that incorporate a ketomethylene unit in place of a native amide link. Key CC bond forming steps involve the stereocontrolled addition of a functionalised allylsilane to activated sugar derivatives and the asymmetric phase-transfer alkylation of a glycine imine. Utility of this chemistry is demonstrated by the synthesis of a C-analogue of the glycopeptide core found in nephritogenoside. Regioselective ozonolysis of a 1,5-diene is also described.