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

Abstract

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. Dynamic ¹H 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 ¹H n.m.r. time scale at room temperature and probably involves propeller-like conformations (9a)⇌(9b) as the enantiomeric groundstate 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.