DISTORTION IN THE STRUCTURES OF 5-AZAADAMANTANONE AND ITS N-OXIDE - IMPLICATION ON DIASTEREOFACIAL SELECTIVITY

Ab initio molecular orbital studies of adamantanone (1), 5-azaadamanta none (2), and 5-azaadamantanone N-oxide (3) show that 2 and 3 have dis torted structures. The torsional angle tau OCC alpha C beta in the C-2 nu symmetric adamantanone 1 is 120.6 degrees. tau OCC alpha C beta is 124.0 degrees in the piperidinedione ring of 3 and 117.8 degrees in t he cyclohexanone ring of 3, indicating a significant distortion. The c orresponding values for 2 are 122.5 degrees and 120.3 degrees indicati ng a slightly distorted structure. These structural results are consis tent with the previously observed pi-facial selectivity in NaBH4 reduc tion of 2 and 3, but contradict with the suggestion that they are symm etrical.