Synthesis of Highly Optically Active Polysulfoxides by Asymmetric Oxidation of Polysulfides

Abstract

Novel highly optically active polysulfoxides having chiral sulfinyl groups in the main chain were prepared by asymmetric oxidation of the corresponding polysulfides by using chiral N-sulfonyloxaziridine (6). The polysulfoxide with the enantiomeric excess up to 91% ee was obtained in good chemoselectivity when the reaction was carried out with 1 equiv of (−)-N-sulfonyloxaziridine, (−)-6, in chloroform at room temperature followed by reflux. The enantiomeric excess was estimated from the 13C NMR spectrum, and the stereochemistry at the sulfur atom was speculated by comparison of CD spectra of the polysulfoxides with that of the model compound ((S)-p-tolyl methyl sulfoxide). This asymmetric oxidation is the first example of introduction of chirality in good enantioselectivity into the main chain of a polymer by polymer reaction, that is, the first example of the control of “tacticity” by polymer reaction. In fact, the shift of the glass transition temperature of the polysulfoxide was observed depending on the change of tacticity of the polymer. The obtained polymer is regarded as one of the first examples of the polymers having heteroatom chirality in the main chain.