Conformation and configurational assignment of cis and trans 3,4-dimethyl-6-t-butyl-5,6-dihydro-2H-thiopyran-S-oxides and S-methyl cations

The assignment of the cis and trans configuration of 3,4-dimethyl-6-t-butyl-5,6-dihydro-2H-thiopyran-S-oxides and S-Methyl cations (2a, 2b), made by 13C and 17O NMR, and by force field calculations. It is shown that the preferred conformation of all compounds is the half chair and that a previous configurational assignment of the S-oxides should be reversed.