5.37 g of crude 2,3,5-tri-O-benzoyl-1-O-methyl-L-ribofuranose synthesized from L-ribose (1.0 g; 6.66 mmol) in accordance with the method described in Helvetica Chimica Acta 1959, (121), 1171-1173p was added to a 100-ml flask. Thereafter, acetic anhydride (3.73 ml; 5.95 equivalents) and acetic acid (1.60 ml; 2.80 equivalents) were added thereto. The obtained mixture was cooled on ice, and thereafter, concentrated sulfuric acid (530 μl; 1.5 equivalents) was slowly added dropwise thereto. After completion of the reaction for 30 minutes, cold water (50 ml) was slowly added dropwise to the reaction solution, and an upper aqueous layer was separated. The precipitated semi-oily solid was dried under reduced pressure. Thus, 3.97 g of crude 1-O-acetyl-2,3,5-tri-O-benzoyl-L-ribofuranose was obtained in the form of a light yellow oily solid. The obtained solid was analyzed by HPLC. As a result, the ratio of α-/β-anomers in the crude 1-O-acetyl-2,3,5-tri-O-benzoyl-L-ribofuranose was 35/65, and the reaction yield of the β-anomer from the total 3 steps was 56%.
