Synthesis of methyl alpha-L-vancosaminide

The synthesis of methyl alpha-L-vancosaminide from di-O-acetyl-L-rhamnal is described. The allylic alcohol methyl 2,3,6-trideoxy-3-C-methyl-alpha-L-threo-hex-2-enopyranoside was prepared from the glycal, 1,5-anhydro-1,2,6-trideoxy-3-C-methyl-L-ribo-hex-1-enitol, and converted to its N,N-dimethylisourea derivative. The cis amino alcohol functionality in vancosamine was introduced by the electrophilic cyclization of the isourea, followed by hydrolysis of the resulting oxazoline.