Stereodivergent Synthesis of Iminosugars from Stannylated Derivatives of (<i>S</i>)‑Vinylglycinol

An original access to iminosugars from a <i>cis</i>/<i>trans</i> mixture of stannylated oxazolidinones <b>5</b> is reported. The dehydropiperidines <b>7</b>-<i>trans</i> and <b>7</b>-<i>cis</i> were obtained stereoselectively with an <i>RS</i> and <i>SS</i> configuration depending on the order of the Sn–Li transmetalation (followed by electrophilic trapping) and of the ring closing metathesis reactions due to the stereoselective epimerization of the α-aminoanion intermediate. The dehydropiperidines <b>7</b>-<i>trans</i> and <b>7</b>-<i>cis</i> were subsequently used for the synthesis of enantiopure homonojirimycin analogs.