Conformational behaviour of medium-sized rings. Part 13. 5,18- dihydro- and 5,11,12,18-tetrahydrotribenzo[b, f, j][1,4]diazacyclodode- cine-6,17-diones

The unsaturated (3) and saturated (6) bislactams have been prepared from condensations of o-phenylenediamine with the bisacyl chlorides (1) and (2) derived from trans-stilbene-2,2′-dicarboxylic acid and bibenzyl-2,2′- dicarboxylic acid, respectively. Dynamic¹H n.m.r. spectroscopy demonstrates that the 5,18-dibenzyl derivative (5) of (3) and the 5,18-dimethyl- (7) and 5,18 -dibenzyl- (8) derivatives of (6) adopt enantiomeric non-planar conformations with averaged C₂ symmetry in solution. In the case of the two 5,18-dibenzyl derivatives (5) and (8), ring inversion is shown to be slow (ΔG‡ = 20.4 and 21.1 kcal mol⁻¹, respectively) on the^XH n.m.r. time scale at room temperature and probably involves propeller-like conformations (9a) ⇋ (9b) as the enantiomeric ground- state conformations. Both the 5,18-dimethyl- (7) and -dibenzyl (8) derivatives of the saturated bislactam (6) form 1:1 inclusion compounds, (7) with o-xylene and (8) with ethanol.