Optical Resolution, Absolute Configuration and Empirical Force-Field Calculations of (.+-.)-5,8,15,18-Tetramethyl-2,11-diaza(3.3) paracyclophane.

Partial resolution of the title compound 2 into its optical antipodes was achieved by enantioselective chromatography on triacetylcellulose. The absolute configuration of the enantiomers has been tentatively assigned on the basis of their CD spectra. Empirical force-field calculations were performed to characterize the minimum energy conformers of 2 and it was found that the two C2 symmetrical isomers are ca. 3.7 kcal mol–1(15.5 kJ mol–1) more stable than those of Ci and C1 symmetry. Calculated geometrical parameters of one C2 symmetrical conformer of 2 are in good agreement with those found by single-crystal X-ray analysis of the N,N′-ditosylparacyclophane precursor 1. The barrier to racemization has been estimated to be >35 kcal mol–1(> 146.5 kJ mol–1).