Thermal racemisation of N-unsubstituted and various N-substituted S-o-methoxyphenyl S-phenyl sulphimides by pyramidal inversion
Abstract
The rates of the thermal racemisation by pyramidal inversion of optically active N-unsubstituted and N-substituted S-o-methoxyphenyl S-phenyl sulphimides have been measured. In the case of N-arylsulphonylsulphimides [Ar1S (:NSO2Ar2)Ar3] and N-acylsulphimides [Ar1S(:NCOR)Ar2], the electron-withdrawing group (Ar2 or R) retarded the rate of pyramidal inversion. In keeping with the observed trend, the enormous rate differences among the sulphoxide, the sulphimide, and the sulphonium ylide, each having a semi-polar bond, are considered to be predominantly due to the differences of electronegativities of the atoms bonded to sulphur (O 3.5, N 3.0, C 2.5). Intramolecular hydrogen bonding between the oxygen atom of the o-methoxy-group and the hydrogen atom of the imino-group plays an important role in the pyramidal inversion of S-o-methoxyphenyl S-phenyl sulphimide. A correlation has been found between the pyramidal inversion and the i.r. stretching frequency (νS–N,) of the SIV–N bond of sulphimides.