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 bisalkylthio(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)bis2-ethoxy-2, 3-dihydro-5-S-methyl or benzyl 1, 3, 4-thiadiazole] ( 7 ) or ( 8 ).