Cationic ring‐opening polymerization of 1,4‐anhydro‐2,3‐di‐O‐benzyl‐α‐L‐arabinopyranose and synthesis of L‐arabinofuranan

Abstract 1,4‐Anhydro‐2,3‐di‐ O ‐benzyl‐α‐ L ‐arabinopyranose (=1,5‐anhydro‐2,3‐di‐ O ‐benzyl‐β‐ L ‐arabinofuranose) (ABAP) was synthesized and underwent cationic ring‐opening polymerization with several kinds of Lewis acids. All the polylmers prepared by Lewis acids as catalyst were found to consist of two different structural units, α‐furanosidic and β‐furanosidic units, and the structure of the polymers greatly depended on the polymerization conditions. Polymerization of ABAP with antimony pentachloride catalyst at 0°C for 42 h gave a polymer with the highest α content of 93%, and that at −20°C for 3 h gave a polymer with the lowest (25%) α content. The other catalysts such as phosphorus pentafluoride, boron trifluoride etherate, niobium pentafluoride, and tantalum pentafluoride also afforded polymers with mixed structure of α‐and β‐furanosides. After debenzylation of poly(ABAP), a new polysaccharide, L ‐arabinofuranan was obtained.