Conformational preferences of O-substituted oxacalix[3]arenes

A tripicolyl derivative of p-tert-butyloxacalix[3]arene has been synthesized and characterized. The compound crystallizes, as the 0.5 CH3OH . 0.5 H2O complex, in the monoclinic space group P2(1)/c with a = 14.158(7), b = 14.196(7), c = 27.612(12) Angstrom, beta = 103.53(1)degrees, and D-c = 1.083 g cm(-3) for Z = 4. Refinement based on 8738 observed reflections gave a final R value of 0.062. The tris(diethylacetamide) derivative of t-butyloxacalix[3]arene has been prepared in high yield and structurally characterized in two forms. A desolvated form crystallizes in the monoclinic space group P2(1)/n with a = 22.062(2), b = 11.028(11), c = 22.357(3)Angstrom, beta = 103.78(1)degrees, and D-c = 1.152 g cm(-3) for Z = 4. Refinement based on 6284 observed reflections gave a final R value of 0.107. A solvated compound crystallizes with 2 molecules of DMF in the triclinic space group P-l with a = 13.5598(6), b = 13.6343(5), c = 19.3443(9) Angstrom, a = 76.938(1), beta = 77.873(1)degrees, gamma = 61.699(1)degrees, and D-c = 1.159 g cm(-3) for Z = 2. Refinement based on 8414 observed reflections gave a final R value of 0.064. Conformational preferences of these compounds have been modelled by computational methods. The results of these simulations support the ratios of cone:partial cone conformers found experimentally.