Nucleophilic displacement reactions in carbohydrates. Part XIV. The reaction of 2,3-O-isopropylidene-5,6-bis-O-methylsulphonyl-α-D-mannofuranose with sodium methoxide: a route toL-allose derivatives

Abstract

On brief treatment with methanolic sodium methoxide, 2,3-O-isopropylidene-5,6-bis-O-methylsulphonyl-α-D-mannofuranose (5) is converted into methyl 5,6-anhydro-2,3-O-isopropylidene-β-L-allofuranoside (8) whereas prolonged treatment gave methyl 2,3-O-isopropylidene-6-O-methyl-β-L-allofuranoside (9). The reaction is considered to proceed with the initial formation of 4,5-anhydro-2,3-O-isopropylidene-6-O-methylsulphonyl-aldehydo-L-gulose (6), which undergoes epoxide ring-opening with aldehyde-group participation to give methyl 2,3-O-isopropylidene-6-O-methylsuphonyl-β-L-allofuranoside (7). The latter sulphonate is then transformed under the basic conditions into the products observed. The anhydro-sugar (8) is a valuable precursor of L-allose derivatives. A route to 6-amino-6-deoxy-D-allose derivatives is also described.