An approach to the stereocontrolled synthesis Of beta-D-rhamnopyranosides is described in which 2,3-O-benzyl or related 4,6-O-[alpha-(2-(2-iodophenyl)ethylthiocarbonyl)benzylidene]-mannosyl thioglycosides are first used to introduce the beta-D-mannopyranoside linkage in high yield and stereoselectivity. Following glycosylation, treatment with tributyltin hydride in toluene at reflux brings about reductive radical fragmentation directly to the 6-deoxy sugar in high yield. A variation of these donors bearing a carboxylated donor on O-3 is a highly alpha-selective mannosyl and, after radical fragmentation, alpha-D-rhamnosyl donor. Using this stereoselective glycosylation/radical-fragmentation approach, a concise synthesis of the title tetrasaccharide is realized in which both the beta-D- and alpha-D-rhamnopyranosyl units are obtained in a single step by a double radical fragmentation of the modified benzylidene acetals.