Computational study of the effect f configura ion a - nd he degree o substitution at N in N - ? 0 a d - ? i \ I acyl migration in dias

Using molecular mechanics (MM2, MM3) and semiempirical molecular orbital methods (EHMO, AMI, PM3) the relative energies were estimated from models for the tetrahedral intermediates in N->0 and o~N acyl migration in diastereoisomers of 3-amino-1,2,3triphenylpropanol to check the necessity of invoking a stereoe!ectronic effect to explain their reactivities . The molecular mechanics results correctly reproduce the greater steric hindrance expected from phenyl/OH and phenyl/CH3 diaxial interactions in the models for the tetrahedral intermediates of the reactions for converting the rel-(1R,2S,3R)-3acetamido-l,2,3-triphenylpropanol and, respectively, rel-( 1R,2S,3S)-3(N-methylaceta-mido )-1,2,3triphenylpropanol, into the corresponding amino and methylamino esters. Results from computations with the COSMO continuum salvation model, as applied to the semiempirical AM 1 Hamiltonian, show that in all cases the intermediates with the N H, respectively N-CH3, axial are stronger stabilized by the solvent, thus casting doubt on the exclusive role of the stereoelectronic effect in this case.