Transformations involving 6-ring transitional intermediates

Abstract

possible conformations, Ilia and IIIb, both of which Intermediates possess unfavorable phenyl-hydrogen interactions. The importance of non-bonded interactions in the transition state of transformations involving substituted 1, 2-ethanolamines has been extensively demonstratedL Recently STOHMER and FRaY z have applied these considerations in the assignment of configuration to the isomeric 1,3-diphenyl-3-amino 1-propanol s. These authors observed that only the fl-isomer in the form of its N-acetyl derivative undergoes N-> O acyl migration under acidic conditions whereas the ~-isomer on successive treatment with phosphorous pentachloride and water is converted irreversibly to the fl-isomer 3. On the basis of these observations and in analogy with the established specificity of these transformations in the

Conformational analysis and chemical reactivity

“…An interesting explanation of this and related type reactions has been given by Traynham (21). 1,3-cf s-cy cl i zation reactions are also dependent on certain conformational aspects (22). These type reactions are of interest since they proceed through nonplanar transition states.…”

“…For example, under acidie conditions only the erythro isomer of the l,3-diphenyl-3-amino 1-propanols undergoes anN-t-0 acyl migration reaction (22). As seen in Figure 7, the transition state for reaction of the erythro isomer contains the two phenyl groups in equatorial positions and therefore will be more stable than the would-be transition state for reaction of the threo isomer where one of the phenyl groups occupies an axial position, Even though an estimate of the relative stabilities of the ground states of the erythro and threo isomers is obscured somewhat by the separation of the two end carbons by a methylene group, one would still predict that the difference in energy of the ground states will be less than the difference in energy of the corresponding transition states.…”