The synthesis of disaccharides containing sulfur in the reducing ring through a nonglycosylating chemical strategy is described. Lactose, maltose and cellobiose were transformed in several steps into the appropriately protected 4-O-glycosyl-2,3-O-isopropyliden-aldehydo-d-glucose dimethyl acetals (6, 11, 18 and 27) and 4-O-glycosyl-2,3-Oisopropyliden-aldehydo-l-idose dimethyl acetals (42 a and 42 b). Compounds 6, 11, 18 and 27 were converted into the corresponding 4-O-glycosyl-5,6-dideoxy-5,6-epithio-2,3-O-isopropylidene-aldehydo-l-idose dimethyl acetals 33 e ± h via the 5,6-cyclic sulfates 31 a ± d, by reaction with potassium thioacetate or potassium thiocyanate and treatment with NaOMe/MeOH. Nucleophilic ring opening of the episulfide ring of 33 e ± h, with sodium acetate followed by acidic hydrolysis, Zemple  n de-O-acetylation and acetylation gave the thio disaccharides 4-O-(2',3',4',6'-tetra-O-acetyl-b-d-galactopyranosyl-, -a-d-glucopyranosyl-and -b-d-glucopyranosyl)-1,2,3,6-tetra-O-acetyl-5-thio-a,b-l-idopyranoses (38 ± 40). 1,2,3-Tri-O-acetyl-4-O-[2',3',4',6'-tetra-Oacetyl-b-d-galactopyranosyl]-6-deoxy-5thio-a,b-l-idopyranose (37) was obtained by treatment of 4-O-(2',6'-di-Oacetyl-3',4'-O-isopropylidene-b-d-galactopyranosyl)-2,3-O-isopropylidene-6-Scyano-5-O-sulfonate-6-thio-aldehydo-dglucose dimethyl acetal potassium salt (32 a) with lithium aluminium hydride followed by acidic hydrolysis and acetylation. The analogous thio maltose and cellobiose (47 c and 47 d) were synthesised following a similar strategy (5,6cyclic sulfate 3episulfide 3thiosugar) from compounds 42 a and 42 b.