Static and Dynamic Stereochemistry of N-(1,4-Dimethyl-9-triptycyl)hydroxylamine Derivatives

Static and dynamic stereochemistry of N-alkyl, O-alkyl, and N,O-dialkyl derivatives of N-(1,4-dimethyl-9-triptycyl)hydroxylamine were studied. X-ray crystallographic analysis revealed that an N-alkyl derivative adopts R*-(-sc)* conformation while N,O-dialkyl derivatives adopt R*-ap conformation. In solution, stereomutation was almost frozen on the NMR timescale at ca. -60 °C. The same conformer as found in the crystal was the major conformer in solution in each compound, and a small amount of a second conformer was found in equilibrium with the major one for the N-alkyl and N,O-dialkyl derivatives. The stereomutation was interpreted in terms of diastereomerization and enantiomerization, and the 1H NMR lineshape analysis afforded the activation parameters for these processes.