The first successful synthesis of bicyclic 2,4-oxazolidinediones with bridgehead nitrogen, examples of anti-Bredt imides, was accomplished. The synthetic approaches involved three homologous bridging sizes, and the smallest product capable of preparation was l-aza-8,9-dioxo-7-oxa-6-phenylbicyclo[4.2.1]nonane, for which the structure was verified by X-ray diffraction. Also prepared was l-aza-9,10-dioxo-8-oxa-7-phenylbicyclo[5.2.1]decane. These results were accurately predicted by using anti-Bredt olefins as models, suggesting that resonance effects may be essential for the stability of anti-Bredt imides. © 1984, American Chemical Society. All rights reserved.