Stereoelectronic effects in cyclic sulfoxides, sulfones, and sulfilimines: Application of the Perlin effect to conformational analysis

The (1)J(C-H) coupling constants in conformationally constrained sulfoxides, bissulfoxides, sulfoxide-sulfones, and sulfilimines derived from 2-benzylidene-1,3-dithiane and 2-(2,2-dimethylpropylidene)-1,3-dithiolane were measured by means of HMQC and HSQC NMR experiments and the Perlin effects were calculated. The type and the relative configuration of S-X groups (X= O, NTos) in these compounds have a strong influence on the magnitude of coupling constants for axial and equatorial C-H bonds, respectively. Axial S=O bonds give rise to a stereoelectronic effect on antiperiplanar axial C-H bonds. The resultant weakening of the respective C-H bonds leads to a smaller coupling constant than for a respective equatorial C-H bond. Equatorial S=O groups have an influence on beta-C-H bonds through a homoanomeric effect. Here, the axial C-H bond is weakened and a smaller coupling constant is measured. Sulfilimine groups show similar effects to sulfoxide groups.