Asymmetric synthesis of optically active di‐isotactic polymers from cyclic monomers

A new asymmetric synthesis of polymers is described; it was obtained from monomers which do not contain asymmetric carbon atoms. The polymerization, in the presence of asymmetric cationic catalysts, of an unsaturated cyclic compound, benzofuran, by opening of the double bond of the furan ring, led to polymers having high optical activity. The rotation dispersion curve, which shows a maximum at 303 mμ ([M] = –800) is here shown. Each monomeric unit of these polymers contains two carbon atoms in the chain, which are asymmetric, even if considered in their immediate surrounding. Optically active polybenzofurans do not remarkably contain asymmetric end‐groups deriving from the catalyst. The asymmetric synthesis may therefore be related to the orienting effect of the negative asymmetric counter‐ion.