Cationic ring-opening polymerization of 1,6-anhydro-2,3,4-tri-O-allyl-beta-D-glucopyranose as a convenient synthesis of dextran

For the convenient synthesis of (1-->6)-alpha -D-glucopyranan, i.e., dextra n (4), ring-opening polymerization of 1,6-anhydro-2,3,4-tri-O-allyl-beta -D -glucopyranose (1) has been carried out using BF3. OEt2. With a ratio of [B F3. OEt2]/[1] = 0.5 at 0 degreesC for 140 h, the yield and (M) over bar (n) of the obtained polymer are 84.0% and 21 700, respectively. The polymer co nsists of (1-->6)-alpha -linked 2,3,4-tri-O-allyl-D-glycopyranose (2) which is similar to the results for the cationic ring-opening polymerization of 1,6-anhydro2,3,4-tri-O-methyl-beta -D-glucopyranose and 1,6-anhydro2,3,4-tr i-O-ethyl-beta -D-glucopyranose. Polymer 2 was iosmerized using tris(triphe nylphosphine)- chlororhodium as the catalyst in toluene/ethanol/water to yi eld polymeric 2,3,4-tri-O-propenyl-(1-->6)-alpha -D-glucopyranan (3). Depro tection of the propenyl ether linkage of 3 was then performed using hydroch loric acid in acetone to give 4.