Reactions of ethyl 3,5,6-tri-O-acetyl-2-S-ethyl-1,2-dithio-α-D-mannofuranoside with halogens

Ethyl 3,5,6-tri-O-acetyl-2-S-ethyl-1,2-dithio-α- D -mannofuranoside (5) reacted with bromine to give the very unstable glycosyl bromide 4, which with water gave a mixture of the 1-hydroxyl analogue (8) and the nonreducing α- D -(1→1)-linked disaccharide derivative 9. When the bromide 4 was treated with mercuric acetate or potassium acetate, 1,3,5,6-tetra-O-acetyl-2-S-ethyl-2-thio-α- D -mannofuranose (7) was obtained, but silver acetate in carbon tetrachloride gave 7 in admixture with its β-anomer (10). Methanol reacted with 4 to give an anomeric mixture of the glycofuranosides (11 and 12). An excess of chlorine converted the dithio derivative 5 into a 3,5,6-tri-O-acetyl-2-chloro-2-S-ethyl-2-thio- D -manno(or gluco)furanosyl chloride (13), whereas a lower proportion of chlorine appeared to give the 1-chloro analogue of 4. Treatment of the dichloro derivative 13 with methanol led to a mixture of three methyl glycosides, one (14) retaining the chlorine atom at C-2, and the other two (15 and 16) resulting from exchange of both chlorine atoms by methoxyl groups.