3,4-Di-tert-butyl-1,3,4-oxadiazolidine: synthesis and structure

3,4-Di-tert-butyl-1,3,4-oxadiazolidine 1d has been synthesized and for the first time fully characterized; an envelope conformation has been established by X-ray diffraction analysis of 1d in the crystal, and a semi-chair conformation with a trans-diaxial orientation of Bu^t groups determined by NMR spectroscopy in solution and, additionally, by MNDO and ab initio calculations in the gas phase; the lower limit of the barrier to sterically-hindered nitrogen inversion was evaluated as ΔG#symbol_2# > 22.8 kcal mol^-1 at 130^oC.