Dithiane S-oxide

Conformational Analysis of Dithiane S-Oxides 3.4.1 1,2-Dithiane S-Oxide 

In fact, the equilibrium (23-ax) (23-eq) is so much tilted to the left that the 

Nevertheless, it has been demonstrated by Lambert et al. [22] that the introduction of a gem-dimethyl group at C-3 in thiane-l-oxide to afford (5) strongly disfavours the axial conformer (see Section 3.2.2). For example, comparison of the conformational equilibria in 1,3-oxathiane 5-oxide (17) and 5,5-dimethyl-l,3-oxathiane 5-oxide (18) suggests that the magnitude of the syn-diaxial CH3/S=0 interaction amounts to 1.3kcalmol [55] (see Section 3.3.2). 

The very large difference in chemical shifts for the hydrogen atoms at C-3 (A8 = 1.45 ppm) [66] was attributed to a predominantly axial conformation in (24), in which H-3ax experiences a strong deshielding effect by the syn-diaxial sulfinyl group. 

In an attempt to observe different signals for the individual conformers in the (24-ax) (24-eq) equilibrium, the spectrum was recorded at -80°C in CD2CI2. 

---