Optical resolution, absolute configuration and empirical force-field calculations of (±)-5,8,15,18-tetramethyl-2,11-diaza[3.3]paracyclophane

Abstract

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 C_i 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).