One-step syntheses of p- and m-xylylene-bridged azacalixarenes and their rigid molecular skeletons

Novel self-filled azacalixarenes were synthesized following a simple method . The structure of a. p-xylylene-bridged compound was investigated by Xray crystallographic analysis. Compound 1:C-42:H-44 O4N2, monoclinic,space grou p C2/c, a = 17.236 (4), b = 9.244 (3), c = 22.217 (4) Angstrom, beta = 101. 23 (1)degrees, D-calc 1.226 g/cm(3), V = 3472 (1) Angstrom(3), Z = 4, R = 0 .042. The final cycle of full-matrix least-squares refinement was based on 2201 observed reflections [I>3.00 sigma(I)] and 284 variable parameters. Dy namic NMR and MM3 calculations were also employed to study the structures i n solution. Azacalix[4] skeletons are rigidly fixed in shallow cone conform ations and bridging xylylene units (p- and m-) are located in the cavities of the cyclic skeletons. Intra-cavity hydrogen bonds between OH and N atoms localize at low temperatures. The free energy of the localization was esti mated to be 10.8 and 11.2 kcal mol(-1) for p- and m-xylylene-bridged compou nds, respectively.