DISORDER VERSUS SYMMETRY IN THE HELICAL TUBULAND INCLUSION HOST LATTICE - A SUCCESSFUL TRISHOMOCUBYL DIOL PROBE

New examples of the helical tubuland diol host family may be targeted for synthesis by consideration of structural rules which result:in formation of the specific hydrogen bonding arrangement required. To test crystal engineering requirements of symmetry:arid: substitution in these diols, the 4,7,11-trimethylpentacyclo [6.3.0.0(2,6).0(3,10).0(5,9)]undecane-4,7-diol isomer 8a has been prepared and its X-ray structure determined: [C14H20O2, P3(1)21, a 12.609(2), c 7.209(2) Angstrom, Z3, R 0.032]. This diol is a further example of the helical tubuland family despite it lacking C-2 symmetry. Instead, overall C-2 symmetry results in the solid state by means of crystallographic disorder. The C11 methyl group which is equally disposed over its two possible positions reduces the canal unobstructed cross-sectional area to only 8.9 Angstrom(2), but demonstrates that disruption of the lattice type-can be avoided provided substituents are placed within the parallel canals. These observations now allow prediction of a much wider range of helical tubuland structures. The diol isomer 8b [C14H20O2, P2(1)/c, a 12.795(1), b 6.4608(4), c 15.003(1) Angstrom, beta 111.846(4)degrees, Z 4, R 0.043] forms a layer structure involving (-OH)(4) cycles in common with other diols of closely related structure.