N-Substituted 5-aza-2-adamantanones and 5-bora-2-adamantanone have been studied by ab initio MO methods at Becke3LYP level for their diastereofacial selectivities in reactions with nucleophiles by applying the complexation model. The facial predictions are fully consistent with the experiments. This is to be emphasized that in a given substrate there may be centres other than the carbonyl oxygen that may compete for the cation and, thus, contribute to the overall diastereodetermination. Other models such as the Cieplak model. Anh-Felkin model, and Houk model may or may not apply.