A] treating a compound of formula (V) with a cyanogen halide which may be selected from cyanogen fluoride, cyanogen chloride, cyanogen bromide or cyanogen iodide to obtain methyl 5-acetamido-4-cyanamido-6-(1,2,3-triacetoxypropyl)-5,6-dihydro-4H-pyran-2-carboxylate (VIII); B] deacetylating the intermediate (VIII) to obtain methyl 5-acetamido-4-cyanamido-6-(1,2,3-trihydroxypropyl)-5,6-dihydro-4H-pyran-2-carboxylate (IX). The reaction may be carried out in the presence of a deacetylating agent which may be selected from the group consisting of methanol/iodine, methanol/water, sodium t-butoxide, potassium carbonate, sodium hydroxide, or sodium methoxide; C] hydrolyzing the compound (IX) in a basic medium to obtain 5-acetamido-4-cyanamido-6-(1,2,3-trihydroxypropyl)-5,6-dihydro-4H-pyran-2-carboxylic acid of formula (VII). The base used in the reaction may be organic or inorganic. The organic base may be selected from the group consisting of pyridine, dimethylamine, trimethylamine and sodium ethoxide. The inorganic base may be selected from the group consisting of sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, sodium bicarbonate and potassium bicarbonate; and D] reacting the compound (VII) with ammonium formate in the presence of ammonia which may be in the form of gaseous ammonia, liquid ammonia or aqueous ammonia and at a high temperature, for example ranging from 80° C. to 100° C., to obtain zanamivir (I).
