Stereochemistry of the conventional and modified BuchererBergs reactions of 2-substituted cyclohexanones

The configurations of the spiro-hydantoins produced from 2-methyl- and 2-phenylcyclohexanone, 2,6-dimethylcyclohexanone, and dl-menthone by either the conventional Bucherer–Bergs (B • –B • ) reaction, or a variant employing COS or CS 2 in place of CO 2 , have been established by 13 C nmr. In all cases the conventional B • –B • reaction gave the hydantoin having the 4′-carbonyl group equatorial, and the COS or CS 2 variant, the mono- or dithiohydantoin having the 4′-thiocarbonyl group, axial.