Synthesis of polysaccharides. Communication 7. The cationic polymerization of 1,2,4-orthoacetyl-3-O-acetyl-α-D-xylopyranose

1.	The cationic polymerization of l,2,4-orthoacetyl-3-O-acetyl--D-xylopyranose (I) was initiated by various electrophilic reagents was studied in various solvents and at different temperatures. The greatest yield of polysaccharide and the least yield of side products in the range of conditions studied was achieved in the polymerization with triphenylcarbonium perchlorate at –21° in methylene chloride.
2.	The side product, 2,3-di-O-acetyl-l,5-anhydro--D-xylofuranose (II) which is formed in the isomerization of orthoester (I) also undergoes cationic polymerization or copolymerization with orthoester (I) under the conditions used. Under the optimal conditions for the polymerization of the orthoester, the participation of the anhydride in the formation of the polysaccharide is insignificant.
3.	Silver salts may serve as powerful initiators of cationic polymerization of both orthoester (I) and of anhydride (II) in the presence of orthoester (I).