Trans‐2‐isopropyl‐1,3‐dithiane‐l‐oxide; a conformationally fixed isopropylgroup

Abstract

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.