The stereochemical relationship between the C-2 and C-3 alcohols may well affect the ease with which the carbonate can be formed (Figure ). As shown in structure 7c, sugars with anti stereochemistry at C-2/C-3 (e.g. D-rib) will have to form the more sterically hindered syn-cyclic carbonate. This hindered carbonate may also hinder alignment of the C-1 proton into the correct orientation for the subsequent E-2 elimination. In contrast, sugars with synstereochemistry at C-2/C-3 (L-ara) will form the less-hindered anti-cyclic carbonate (e.g. 7a) which can easily adopt the required conformation for E-2 elimination to generate the alkene. Preliminary DFT calculations suggest that the formation of the syn carbonate 7c from 5c is ~20.5 kJmol -1 more endergonic than the formation of the anti carbonate 7a from 5a. Attempts to use more reactive electrophiles such as (CDI) carbonyldiimidazole with 5c failed to give any improvement in the yield, indicating that the stereochemical relationship in these starting materials presents a significant barrier to successful dehydration under mild reaction conditions. An alternative strategy was therefore considered for antisugars which did not rely on the formation of a cyclic intermediate. It was envisaged that conversion of the thioacetal 5c to the corresponding peracetate could lead to sufficient activation of the C-2 alcohol for it to act as a leaving group, facilitating dehydration under basic conditions. Formation of the peracetate derivatives with pyridine/Ac2O, prior to treatment with a base was explored for the D-ribose, L-rhamnose and D-mannose thioacetal derivatives (Scheme 5).