NOVEL MACROCYCLES INCORPORATING CYCLIC UREA UNITS

The reaction of 1,3- and 1,4-bis(bromomethyl)benzenes with 5-tert-butyltetrahydro-1,3,5-triazin-2(1H)-n-one (1) and 2-imidazolidone (2) has been used to synthesize a series of 16- and 18-membered ring calixarene analogs which incorporate cyclic urea units. The structures and conformations of these novel macrocyclic ring systems have been investigated in the solid state by X-ray crystallography and in solution by various NMR methods. The results indicate important conformational equilibria dominated by species having syn and anti alignments of the urea carbonyl groups and that interconversion of these conformers likely occurs by carbonyl through the annulus rotation. AM1 semiempirical molecular orbital geometry optimizations are consistent with these findings.