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(S4bis) , 8-9000 GHENT (Belgium).Received 91 1/77 -Accepted IOl3177. Abstract.Three thianes substituted with a *-a',y'-diMe holding group and with i n the 6-ringposit i o n of sulfur a C-. 0-and S-atom respectively have been oxidized with a v a r i e t y of oxidants and the i s w e r i c d i s t r i b u t i o n s of the r e s u l t i n g mono-sulfoxides have been analyzed by gaschromatography.s t r a i n t s from r i n g substituents and t o the e l e c t r o n i c f e a t u r e s of the s u b s t r a t e molecules.The stereochemistry of these oxidations appears t o be s e n s i t i v e t o s t e r i c con-

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It is found by ' H n.m.r.spectroscopy that in --2-isopropyl-l,3-dithiane-1-oxide an S-0 : C-Me synaxial type of interaction is relatively disfavoured, having its impact in the rotameric behaviour of the isopropylqroup.It has been shown' that introduction of a 3,3-dimethyl-grouping in thiane-1-oxide reverses the original axial preference of the sulfoxide function into a pronounced equatorial one. Recently we have demonstratedl that a similar repulsive interaction occurs in 5,5-dimethyl-1,3-dithiane-l-oxide (&I.Whereas Q) exclusively occurs in the SO-equatorial conformation, the parent unsubstituted oxide (2) contains 15% of the axial form Za at -92OC.