The previously unknown (2R,6R)-2[(tertbutyl)diphenylsilyloxyl-6-propa-1,2-dienyl-2H-pyran-3(6H) -one (16) was derived from tri-O-acetylglucal. Conjugate addition of PhSAlMe2 to 16 followed by enolate trapping with 1,2-O-isopropylidene-3-O-methyl-alpha -D-xylo-pentodialdo-1,4-furanose and NaBH4 reduction of the intermediate aldol furnished a new C-glycoside of a C-disaccharide: 4,8-anhydro-9-O-[(tert-butyl)diphenylsilyl]-6-[(5R)-1,2-O-isopropylidene -3-O-methyl-alpha -D-xylo-furanos-5-C-yl]-5-S-phenyl-1,2,3,6-tetradeoxy-5-thio-D-glycero-L -gulo-none-1,2-dienitol (24). Similarly, conjugate addition of PhMe2SiZnMe2Li to 16, followed by cross-aldol reaction with 2,6-anhydro-1,3,4,5-tetra-O- [(tert-butyl)dimethylsilyl]-D-glycero-L-manno-heptose (27), and reduction gave either 4,8-anhydro-6-{(1S)-2,6-anhydro-3,4,5,7-tetra-O-[(tert-butyl)dimethylsil yl-D-glycero-L-manno-heptitol-1-C-yl)-9-O-[tert-butyl)diphenylsilyl]-1,2 ,3,5,6-pentadeoxy-5-phe nyldimethylsilyl-D-glycero-D-manno-(29) or L-gulo-nona-1,2-dienitol (30).