Selective cyclisation of 2, 3, 4, 5-tetra-O-acetyl-galactaric acid bis-[Alkylthio(thiocarbonyl)]hydrazide to Saccharide 1, 3, 4-Oxadiazole, Thiadiazole, and thiadiazoline derivatives

The synthesis of galactaric acid acetate bis[alkylthio(thiocarbonyl)]hydrazide (1, 2) is described. Selective cyclisation of both hydrazides 1 and 2 was investigated. Phosphorous oxychloride as cyclising agent led to dehydrative cyclisation and produced 1, 2, 3, 4‐tetra‐O‐acetyl‐1, 4‐bis(5‐S‐methyl or — benzyl) 1, 3, 4‐thiadiazol‐2‐yl galactotetritol (3) or (4). While thionyl chloride led to dehydrosulfurization and gave 1, 2, 3, 4‐tetra‐O‐acetyl‐1, 4‐bis(5‐S‐methyl or ‐benzyl)‐1, 3, 4‐oxadiazol‐2‐yl galactotetritol (5) or (6). Finally with triethyl orthoformate as cyclising agent, compounds 1 or 2, gave 3, 3′‐(2, 3, 4, 5‐tetra‐O‐acetyl‐galactar‐1.6 dioyl)bis[2‐ethoxy‐2, 3‐dihydro‐5‐S‐methyl or benzyl 1, 3, 4‐thiadiazole] (7) or (8).