Heterocalixarenes Part 3: Bis-oxo-bridged calix[1]cyclicurea[3]arene and calix[1]cyclicurea[1]pyridine[2]arenes. Synthesis, X-ray crystal structure and conformational analysis

The Friedel-Crafts aroylations of 2- and 4-methylanisole with isophthaloyl dichloride or pyridine-2,6-dicarbonyl dichloride provide respective diones, which on bromination with NBS provide corresponding bisbromomethyl derivat ives that undergo simple cyclocondensations with embedded cyclicurea-contai ning heterocycles, viz. benzimidazol-2(1H)-one, 5-nitrobenzimidazol-2(1H)-o ne, 5,6-dinitrobenzimidazol-2(1H)-one, uracil and quinazoline-2,4(1H,3H)-di one to form 11 new bis-oxo-bridged heterocalix[4]arenes (11-19, 24, 25). Th e X-ray crystal structure of the 11-benzene complex, H-1-H-1 COSY spectra a nd energy-minimization studies assign partial cone conformations to these h eterocalix[4]arenes. The variation in the cyclicurea moiety controls the fl exibility of these heterocalix[4]arenes.