SIN CHEONG WONG. Can. J. Chem. 57,1456 (1979.The tropane-3-spiro-5'-hydantoin (a isomer) obtained from tropinone by the BuchererBergs reaction has been shown by 13C nmr and X-ray diffraction studies to have the 4'-carbonyl group in the equatorial position; the isomer, obtained via the Strecker reaction, has this group axial. The results of these two reactions on cis-bicyclo[3.3.0]octan-3-one and on cis-3,4-dimethylcyclopentanone show, on the basis of the 'H nmr, 13C nmr, and X-ray diffraction studies of the products, a stereochemical course related to the preferred conformation of the cyclopentane rings.