Regio- and Stereoselective Synthesis of Sulfur-Bearing Four-Membered Heterocycles: Direct Access to 2,4-Disubstituted Thietane 1-Oxides.

Starting from readily available C2-substituted thietane 1-oxides, a straightforward synthesis of new C2,C4-disubstituted thietane 1-oxides has been developed by using a lithiation/electrophilic trapping sequence. The chemical and configurational stability of lithiated C2-substituted thietane 1-oxides has been investigated as well as the stereochemical implications for this process. The results demonstrate that a stereoselective functionalization at the C2, C4 positions of a thietane is feasible, leaving intact the four-membered ring.