A two-step method has been developed to synthesize several biologically important iminocyclitols in ca. 44-60% yields by using Petasis-type condensation. The method is very general and operationally simple, affording a series of iminocyclitols from easily available sugar derivatives. Unexpected diastereoselectivities are observed, suggesting that the condensation may proceed through a five- or six-membered cyclic iminium ion intermediate.