Reaction of 1-aza-3-ethylbicyclo[1.1.0] butane (3) with N2O4 under a variety of experimental conditions afforded several products, 4-7, all of which resulted via addition across the strained central C(3)-Nσ-bond in 3. The corresponding reactions of ClCO2Et, Tf2O, and MS2O with 3 also have been studied. These reactions provide useful methods for synthesizing N-substituted 3-ethylideneazetidines and 2-azetines. © 1994, American Chemical Society. All rights reserved.