Silicon-assisted etherification reactions: application to the synthesis of high-molecular-weight polyethers

The formation of ether bonds by reaction of benzylic bromides with phenyl silyl ethers has been investigated as an alternative to the classical Williamson ether synthesis. The reaction has been applied to the synthesis of high-molecular-weight polyethers that are not readily obtained by other methods. An AB-type monomer, such as 3-bromomethyl-trimethylsilyloxybenzene, reacts in the presence of a stoichiometric amount of carbonate to afford the corresponding polyether with molecular weight as high as 300 000 depending on the reaction conditions. While the polyetherification reaction of 3-bromomethyi phenol under classical conditions leads to polymers rich in C-alkylated and branched units, conditions may be found to reduce or prevent C-alkylation and branching with 3-bromomethyl-trimethylsilyloxybenzene. The reaction is believed to proceed via activation of the OSi bond through carbonate addition to afford a species containing a pentacoordinate silicon. The role of carbonate and the stoichiometry and mechanism of the reaction have been investigated with the help of a model etherification reaction.