From their discovery in the late 1960s, iminosugars have undergone an expansion from an area of science limited to a few researchers to a field that now attracts the interest of members of the whole synthetic organic chemistry community. Indeed, many tasks concern structural modifications of standard iminosugars in order to improve their biological and pharmacological properties. In this way, the introduction of an adjoining spirocycle afforded unprecedented polyhydroxy-azaspiranes, the structures and syntheses of which are presented in this chapter. Special attention is paid to the key steps involved in the generation of the pivotal quaternary spiro atom.