earticle

영어

Benzyl ethers are frequently used ether protecting groups in carbohydrate chemistry. Together with ester groups, they already form the selective protection and deprotection of saccharide building blocks prior to and after the glycosidic linkage step for the synthesis of oligosaccharides. The most general used highly regioselective benzylation means involves the utilization of organotin. The regioselectivity was provided by introduction of dibutylstannylene acetals, which derived from treatment of diols and polyols with organotin. Benzyl bromide was herein used as electrophiles, which was normally performed in the presence of halide anions for the improvement in terms of speed, yield and general convenience. However, the mechanistic origin of the improvement for the reaction by halides has not been fully clarified. In present study, the mechanistic origin as to the promoted organotin-mediated carbohydrate benzylation by halides was explored by the comparison of the activation ability of halides on benzylation of methyl β- D-galactoside. It was demonstrated that the improvement of benzylation in the presence of halides was due to the formation of the activated oxide species by the coordination of the halide anions to the tetracoordinate tin atoms. The halide, being able to form stronger bond with tin, showed stronger activation ability. The results were further applied to more carbohydrate structures and multiple carbohydrate benzylations. A range of prototype carbohydrate structures were efficiently prepared with the guidance of the principle.