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

Abstract

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 derivatives that undergo simple cyclocondensations with embedded cyclicurea-containing heterocycles, viz. benzimidazol-2(1H)-one, 5-nitrobenzimidazol-2(1H)-one, 5,6-dinitrobenzimidazol-2(1H)-one, uracil and quinazoline-2,4(1H,3H)-dione to form 11 new bis-oxo-bridged heterocalix[4]arenes (11–19, 24, 25). The X-ray crystal structure of the 11–benzene complex, ¹H–¹H COSY spectra and energy-minimization studies assign partial cone conformations to these heterocalix[4]arenes. The variation in the cyclicurea moiety controls the flexibility of these heterocalix[4]arenes.