A 1 177 g portion of 2,5-anhydro-3,4,6-tris-O-(phenylmethyl)-D-mannose (prepared in accordance with Example 20) was dissolved in 8.5 ml of methanol and then treated with 5.11 ml of 37% formalin and 480 mg of potassium carbonate. This mixture was heated under argon at 85° C. for 4 hours, then cooled, neutralized with 10% sulfuric acid and evaporated. The residue was taken up in chloroform, washed with brine and evaporated. The residual oil was flash chromatographed, eluting with hexane:ethyl acetate (3:2). The combined fractions gave 860 mg of the desired product, [α]D26 =+37°±2 (c. 0.555, chloroform).
