Enantioselective Access to All-trans 5-Alkylpiperidine-3,4-diols: Application to the Asymmetric Synthesis of the 1-N-Iminosugar (+)-Isofagomine

Access to 3,4-disubstituted N-benzylprolinol derivatives is described that, after optimization of the ring-enlargement reaction conditions, Could be efficiently transformed into the corresponding 3-hydroxypiperidines. This approach was applied to the asymmetric synthesis of (+)-isofagomine relying oil regio- and stereoselective oxirane opening with the cyanide anion of a pivotal epoxypyrrolidine.