3-Substituted thietane derivatives : Stereochemical considerations

Abstract

Stereochemical assignments could be made for a series of 3-substituted thietane 1-oxides from their NMR spectra. Both isomers appear to reside in conformations with the ring substituent equatorial. The cis isomer (equatorial SO bond) is characterized by a large chemical shift difference for the α-methylene hydrogens. The trans isomer is characterized by a significant deshielding of the β-hydrogen (relative to cis isomer, not relative to the parent sulfide). The dominant conformations of 3,3-dimethylthietane 1-oxide and the corresponding 1-tosylimine have the SX bond equatorial. Stereochemical assignments were made to the α-methylene protons and were confirmed by benzene-induced shift data. As expected for a hydrogen anti to the “lone pair” on sulfur the axial hydrogen of the sulfoxide appeared at higher field, the same was not true for the sulfilimine. Significant stereoselective benzene-induced shifts observed for the N-tosylsulfilimine and N-tosylsulfoximine of 3,3-dimetbylthietane indicate that they may constitute a method of configuration assignment for such compounds.