Twist boat conformation of thiane S-oxide both in solid state and in solution

A stable twist boat conformation of thiane S-oxide 1a in solid state and in solution was unambiguously determined by single crystal X-ray crystallography and solution NMR analyses. On the contrary, the thiane Sdioxide 2 which was obtained from the oxidation of corresponding thiane S-oxide 1a was confirmed to adopt a regular chair conformation.