Synthetic Access to the First Spirocyclopropyl Iminosugar

The synthesis of the first spirocyclopropyl iminosugar has been achieved in six steps and 13% overall yield from commercially available 2,3,5-tri-O-benzyl-d-arabinose. The synthesis is based on an efficient two-step reaction involving the titaniummediated aminocyclopropanation of 2,3,5-tri-O-benzyl-4-O-methanesulfonyl-d-arabinononitrile and the subsequent cyclization resulting from in situ nucleophilic attack of the so-formed amine. Addition of a Lewis acid during the cyclopropanationcyclization sequence greatly improved the yields.