α‑Lithiation–Electrophile Trapping of <i>N</i>‑Thiopivaloylazetidin-3-ol: Stereoselective Synthesis of 2‑Substituted 3‑Hydroxyazetidines

α-Lithiation of N-thiopivaloylazetidin-3-ol and subsequent electrophile trapping provides access to a range of 2-substituted 3-hydroxyazetidines with generally good trans-diastereoselectivity, aside from deuteration, which gives the cis-diastereoisomer. Deuterium labeling studies indicate that the initial α-deprotonation occurs preferentially, but not exclusively, in a trans-selective manner. These studies also suggest that the stereochemical outcome of the electrophile trapping depends on the electrophile used but is independent of which α-proton (cis or trans to the hydroxyl group) is initially removed.