NOVEL MACROCYCLES INCORPORATING CYCLIC UREA UNITS

The reaction of 1,3- and 1,4-bis(bromomethyl)benzenes with 5-tert-buty ltetrahydro-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 calixaren e analogs which incorporate cyclic urea units. The structures and conf ormations of these novel macrocyclic ring systems have been investigat ed in the solid state by X-ray crystallography and in solution by vari ous NMR methods. The results indicate important conformational equilib ria dominated by species having syn and anti alignments of the urea ca rbonyl groups and that interconversion of these conformers likely occu rs by carbonyl through the annulus rotation. AM1 semiempirical molecul ar orbital geometry optimizations are consistent with these findings.